Skincare Actives Decoded: Every Category, Mechanism, Concentration & Layering Rule

What A Skincare Active Actually Is (And What It Isn't)

A skincare active is an ingredient with a documented biological mechanism that alters skin function, not just its surface appearance. Emollients, thickeners, preservatives, and fragrance are not actives. They're the delivery vehicle. The active is what does the work; the base formula is the bus it rides in on.

Actives fall into seven core categories organized by mechanism of action: exfoliants, antioxidants, hydrators, barrier-repair agents, brightening agents, anti-inflammatory agents, and anti-aging or acne-targeting actives. Many actives span multiple categories. Niacinamide is simultaneously a barrier-repair active, a brightening agent, and an anti-inflammatory. This overlap is why a single well-chosen active can address multiple skin concerns, and why a poorly chosen one can trigger several problems at once.

Think of actives like tools in a workshop. A hammer is great for nails, terrible for screws. Most skincare frustration comes from using the right active at the wrong concentration, in the wrong base, at the wrong time. The ingredient isn't the problem. The application is.

The Seven Core Active Categories At A Glance

Every skincare active lands in one of seven mechanism-based buckets, though many multi-task across categories. This grid gives you the 30,000-foot view before we zoom into each category's specific actives, concentrations, and compatibility rules.

Exfoliating Actives: AHAs, BHAs, PHAs & Enzymes

Exfoliating actives accelerate desquamation (the shedding of dead skin cells) and cell turnover, targeting texture, dullness, and clogged pores. They fall into four subfamilies: AHAs (water-soluble surface exfoliants), BHAs (oil-soluble pore-penetrators), PHAs (gentler large-molecule acids), and enzyme exfoliants (protein-digesting fruit enzymes). Each subfamily works at a different depth and suits a different skin type.

AHAs: Glycolic, Lactic & Mandelic Acid

Alpha hydroxy acids (AHAs) are water-soluble surface exfoliants that dissolve the bonds between dead skin cells, improving texture and radiance. The three key players differ by molecular size. Glycolic acid (smallest molecule, deepest penetration) is the strongest, best for rough texture but highest irritation potential. Lactic acid (medium molecule) adds humectant hydration on top of exfoliation, making it gentler. Mandelic acid (largest molecule, slowest penetration) is the mildest option, often tolerated by sensitive skin. Smaller molecule equals faster results but higher irritation risk.

Typical OTC concentration ranges: glycolic 5-15% daily, lactic 5-12%, mandelic 5-15%. pH requirements are critical: AHAs need a formulation pH below 4.0 to work. Above that pH, the acid neutralizes and becomes an expensive moisturizer. pH is the first spec to check, before the percentage.

BHAs: Salicylic Acid

Beta hydroxy acid (BHA), specifically salicylic acid, is an oil-soluble exfoliant that penetrates into the pore lining to dissolve sebum and debris. This is the gold standard for clogged pores, blackheads, and oily or acne-prone skin. Unlike AHAs, BHA doesn't need as low a pH, but still performs best in the 3.0-4.0 range. Oil-solubility is the BHA superpower: it goes where the clog is, not just across the surface.

Common OTC concentrations run 0.5-2%; the 2% salicylic acid ceiling is set by OTC regulations. For a deep dive into the AHA vs BHA decision, read our BHA vs AHA comparison. We also break down the cult-favorite Paula's Choice BHA formulation and what makes its 2% salicylic acid different. BHA at 2% daily is the workhorse of pore-clearing routines.

PHAs: Gluconolactone & Lactobionic Acid

Polyhydroxy acids (PHAs), primarily gluconolactone and lactobionic acid, are large-molecule exfoliants that sit on the surface and shed dead cells slowly. Their larger molecular size means slower penetration, dramatically lower irritation, and bonus humectant properties. PHAs are the gentlest acid exfoliant family and can often be used by sensitive and rosacea-prone skin types. Slow and steady exfoliation with a built-in hydration side effect.

Enzyme Exfoliants: Papain & Bromelain

Enzyme exfoliants like papain (from papaya) and bromelain (from pineapple) are proteolytic enzymes that digest the protein bonds holding dead skin cells together. They work only on the very surface, don't alter pH, and are often the best entry point for exfoliation-sensitive skin. The tradeoff: enzymes don't go deep and won't match an AHA or BHA for texture overhaul. Think of enzymes as dusting the surface, while AHAs and BHAs vacuum underneath.

Choosing an exfoliant is like choosing sandpaper grit. Glycolic is 80-grit, fast and aggressive. Lactic is 120-grit, still effective with less risk. Mandelic and PHAs are 220-grit, slow and safe. Enzymes are a microfiber cloth. Pick the grit that matches your skin's tolerance, not the grit the internet told you to buy.

Antioxidant Actives: Free-Radical Neutralizers

Antioxidant actives work by neutralizing free radicals (unstable molecules from UV, pollution, and metabolism) and providing photoprotection that complements sunscreen. They don't replace SPF. They catch what SPF misses. Antioxidants are the secondary shield, not the primary block.

Vitamin C: Ascorbic Acid & Derivatives

L-ascorbic acid is the pure, bioavailable form of vitamin C, backed by decades of data for collagen stimulation, brightening, and photoprotection. The catch: it's unstable in water, oxidizes on contact with light and air, and needs a pH below 3.5 to penetrate. Derivatives like ascorbyl glucoside, tetrahexyldecyl ascorbate, and magnesium ascorbyl phosphate trade some potency for dramatically better stability and lower irritation. Pure L-ascorbic is the performance sedan; derivatives are the reliable commuter car.

Effective concentration range for L-ascorbic acid: 10-20%, with 15% being the sweet spot for most. Below 8%, the brightening and collagen effects drop off sharply. Above 20%, irritation rises without proportional benefit. We analyzed one popular entry in our CeraVe Vitamin C review, looking at the derivative form and the base formula. Check whether your vitamin C product tells you the percentage. If it doesn't, assume it's below 5%.

Vitamin E, Ferulic Acid & The Antioxidant Network

Vitamin E (alpha-tocopherol) and ferulic acid form a synergistic antioxidant network with vitamin C, where each stabilizes the others and multiplies photoprotection. Resveratrol (from grapes), CoQ10 (ubiquinone), and green tea extract (EGCG polyphenols) round out the antioxidant toolkit with additional free-radical scavenging and anti-inflammatory effects. The network effect is real: C+E+Ferulic outperforms C alone by a wide margin in published data.

Hydrating Actives: Humectants & Moisture Binders

Hydrating actives are humectants that pull water into the skin and moisture-binding agents that hold it there. They don't add oil. They don't repair the barrier. They hydrate specifically by attracting and binding water molecules. Hydration is a water story, not an oil story.

Hyaluronic Acid & Its Next-Gen Rivals

Hyaluronic acid (HA) is the most famous humectant molecule, capable of holding up to 1,000 times its weight in water, but its molecular weight determines where it works. High-molecular-weight HA sits on the surface and hydrates the stratum corneum. Low-molecular-weight HA penetrates deeper but can trigger inflammation in sensitive skin. Sodium hyaluronate is the more stable salt form found in most serums. Molecular weight matters more than the percentage on the label.

Newer contenders include polyglutamic acid (holds 4x more water than HA), beta-glucan (oat-derived, also anti-inflammatory), and the old reliables: glycerin (the most studied humectant on earth), urea (humectant + gentle keratolytic at low percentages), and panthenol (provitamin B5, humectant + anti-inflammatory). We compared two popular hydrating serums in our La Roche-Posay Hyalu B5 review. For hydration that also repairs, see how COSRX Snail Mucin combines humectants, barrier support, and soothing in one formula. Also read: snail mucin vs hyaluronic acid, side by side.

Barrier-Repair Actives: The Lipid Replenishers

Barrier-repair actives replenish the skin's lipid matrix and reduce transepidermal water loss (TEWL), the invisible evaporation that dries and sensitizes skin. A compromised barrier is the root cause behind most irritation, sensitivity, and product intolerance. Fix the barrier first, then add actives. Not the other way around.

Ceramides, Cholesterol & Fatty Acids: The 3:1:1 Ratio

The stratum corneum lipid matrix is built from ceramides, cholesterol, and free fatty acids in an approximate 3:1:1 molar ratio. Products that supply all three in this ratio are biomimetic: they match the skin's own architecture. Squalane (the stable, saturated cousin of squalene) mimics the skin's natural oil and absorbs without greasiness. A barrier cream with just ceramides is like a brick wall with bricks but no mortar.

Niacinamide & Peptides: The Barrier Builders

Niacinamide (vitamin B3) is arguably the most versatile active in skincare: it boosts ceramide production, reduces TEWL, brightens, calms inflammation, and regulates sebum, all at once. Effective at 2-10%, with 5% being the most studied concentration for barrier repair. Above 5%, the added benefit is mostly for oil control and pore appearance, not barrier improvement. We break this down in detail at what niacinamide actually does, and compare two budget titans in our Ordinary vs Good Molecules niacinamide analysis. Also: The Ordinary Niacinamide review and Good Molecules Niacinamide review for formulation specifics.

Peptides are short chains of amino acids that signal the skin to produce more collagen, elastin, and structural proteins. Unlike retinoids, which command the skin to renew, peptides send a subtler signal. They're gentler, play well with nearly everything, and work on a longer timeline. Peptides are the marathoners; retinoids are the sprinters.

Brightening Actives: Melanin Regulators

Brightening actives work on melanin regulation and pigment dispersion, interrupting the pigmentation pathway at different points. They don't bleach skin. They slow or redirect melanin production and transfer. Brightening is about evening tone, not whitening.

The Pigment Interrupters

Vitamin C inhibits tyrosinase (the enzyme that triggers melanin production) while also providing antioxidant defense. Niacinamide works downstream by blocking melanosome transfer to surface skin cells, not by stopping production. Alpha arbutin is a stable, gentle tyrosinase inhibitor derived from bearberry, effective at 1-2%. Kojic acid (from mushrooms) inhibits tyrosinase but is less stable and more irritating at effective concentrations of 1-4%.

Licorice root extract (glabridin) and tranexamic acid (3-5%) target different parts of the pigment cascade: licorice soothes while brightening; tranexamic acid interrupts the UV-inflammation-pigment connection specifically in post-inflammatory hyperpigmentation. The key insight: layering brighteners that hit different points in the melanin pathway is more effective than a single agent at higher strength.

Anti-Inflammatory Actives: Redness Reducers

Anti-inflammatory actives calm redness, irritation, and heat by downregulating inflammatory mediators in the skin. They don't treat the underlying cause of inflammation (that's a medical question). They reduce the visible and sensory fallout: flushing, stinging, reactivity. These are calming agents, not cure-alls.

The Calming Toolkit

Centella asiatica (cica, madecassoside) is the star of K-beauty calming formulations, backed by data on wound healing and redness reduction. Green tea polyphenols (EGCG) combine antioxidant and anti-inflammatory action. Allantoin and bisabolol (from chamomile) are classic soothing agents found in barrier creams and post-procedure products. Panthenol (B5) calms and hydrates simultaneously. Colloidal oatmeal is an FDA-recognized skin protectant for itching, dryness, and irritation. Read: best K-beauty calming products for formulations built around centella and green tea.

Anti-Aging Actives: Collagen Stimulators

Anti-aging actives target collagen stimulation, wrinkle reduction, and the visible signs of photoaging through four distinct mechanisms: cell turnover acceleration, collagen signaling, free-radical defense, and epidermal thickening. No single active does all four. A well-built routine stacks them sequentially. Aging is multifactorial. One active can't cover every mechanism.

Retinoids: The Gold Standard

Retinoids are vitamin A derivatives that bind to retinoic acid receptors in skin cells, accelerating cell turnover and collagen synthesis. The retinoid ladder, from strongest to gentlest: tretinoin (prescription only), adapalene (OTC at 0.1%), retinaldehyde (one conversion step from retinoic acid, more effective than retinol), retinol (two conversion steps, the OTC standard), and retinyl esters (three steps, weakest). More conversion steps equal less irritation but slower results.

Typical OTC retinol concentration: 0.01-1%, with 0.3-0.5% being the proven effective range. Start at 0.1-0.3% and titrate up over months, not weeks. Retinoid irritation is cumulative. It shows up on day 10, not day 1. Retinol is the marathon, not the sprint. The damage arrives before the warning light.

Bakuchiol & Growth Factors

Bakuchiol is a plant-derived meroterpene that signals similar collagen pathways to retinol without the same irritation potential or photosensitivity. It's weaker than retinol head-to-head but tolerable for skin that can't handle any retinoid. Growth factors (EGF, TGF-beta) are signaling proteins that direct cell behavior, including repair and collagen production. The data is younger than for retinoids, but the mechanism is plausible. Bakuchiol is the compromise candidate when retinoids are a hard no.

Acne-Targeting Actives: Pore Clearers & Antibacterials

Acne-targeting actives work through two primary mechanisms: unclogging pores (comedolysis) and antibacterial action against C. acnes bacteria. The most effective OTC routines combine a comedolytic with an antibacterial, but timing and separation matter enormously. Stacking acne actives without spacing them is the express lane to a damaged barrier.

The Acne Arsenal

Salicylic acid (0.5-2%) is the OTC comedolytic standard, penetrating pores to dissolve sebum plugs. Benzoyl peroxide (2.5-10%) is the antibacterial workhorse, oxidizing C. acnes directly with no risk of bacterial resistance. Azelaic acid (10-20%) combines comedolytic, antibacterial, anti-inflammatory, and brightening effects in one molecule, making it uniquely suited for acne with post-inflammatory hyperpigmentation. Sulfur (3-10%) absorbs oil and is mildly antibacterial, common in spot treatments. Tea tree oil (5%) has antibacterial activity but needs dilution and carries a higher irritation risk than synthetic alternatives. Benzoyl peroxide and retinoids degrade each other on contact. Use one in the AM, one in the PM.

Formulation Considerations: What Makes An Active Actually Work

An active ingredient's concentration means nothing if the formulation pH, delivery system, and base vehicle don't support its stability and penetration. The first number to check is pH. The second is the base. The third is stability packaging. A 20% vitamin C serum at pH 6 is expensive orange water.

pH Requirements By Active Class

Stability: Light, Air & Heat

L-ascorbic acid is the most notoriously unstable active, oxidizing within weeks in clear, air-exposed packaging. Retinoids degrade under UV light and air exposure; opaque, airless packaging is non-negotiable. Benzoyl peroxide oxidizes other actives on contact, which is why combination BP+retinoid formulations use specialized stabilization. If your vitamin C serum is in a clear dropper bottle and still clear after three months, it never had active ascorbic acid to begin with.

Delivery Systems & Base Formulas

Liposomes and encapsulation technologies wrap actives in lipid shells for time-release delivery, deeper penetration, and reduced irritation. Water-based serums deliver water-soluble actives (vitamin C, niacinamide, HA) fastest. Oil-based formulas carry lipid-soluble actives (retinoids, vitamin E, CoQ10) and seal in hydration. Creams combine both phases for barrier support and sustained release. Gels work well for oily skin and BHA delivery. Toners are the thinnest vehicle, best for mild actives at low concentrations for daily maintenance. The base formula is the delivery truck. Choose the wrong vehicle, and the active never reaches its destination.

Layering & Compatibility: The Rules That Prevent Routine Self-Sabotage

Layering rules are the single most high-stakes variable in an active-heavy routine, because incompatible actives can neutralize each other, irritate the skin, or both. The order of application, timing between layers, and AM/PM split determine whether your routine works or works against itself. More actives in one routine is not ambition. It's impatience wearing a lab coat.

The Golden Layering Order

The universal rule: thinnest to thickest, water-based before oil-based, low pH before high pH. Specifically: cleanser, toner (if used), water-based actives (vitamin C, BHA, niacinamide serums), anhydrous/oil-based actives, moisturizer, occlusive, SPF (AM). Each layer needs 30-90 seconds to dry before the next. Wet skin accelerates penetration and irritation. Let each layer set.

Combo: Vitamin C + Niacinamide

The old warning about vitamin C and niacinamide causing niacin flushing applies only to pure ascorbic acid at low pH mixed directly with niacinamide in the same formula or applied wet-on-wet. In separate, well-formulated products, with dry-down time between them, this combo is safe and complementary. Niacinamide improves barrier function while vitamin C fights free radicals. We unpack the layering specifics at how to layer niacinamide, vitamin C, and BHA. The issue was never the ingredients. It was the impatience between them.

Combo: Retinoids + Moisturizers (The Sandwich Method)

Layering retinoids with moisturizers in a sandwich method (moisturizer, retinoid, moisturizer) reduces irritation without reducing efficacy. The moisturizer buffers the retinoid's absorption rate, not its total effect. This is the standard recommendation for anyone starting retinoids or with sensitive skin. Buffering is not dilution. It's controlled release.

Combo: AHAs/BHAs + Retinoids (Separate Nights)

Applying AHAs or BHAs in the same routine as retinoids doubles the irritation risk and can destabilize the retinoid at low pH. The safe approach: alternate nights, or acids in the AM and retinoids in the PM. If your skin tolerates both on the same night after months of acclimation, apply the acid first (lower pH), wait 20-30 minutes, then apply the retinoid. Most skin doesn't get here. Most skin shouldn't try.

Combo: Benzoyl Peroxide + Retinoids (AM/PM Split)

Benzoyl peroxide directly oxidizes and degrades retinoids on contact, making this the single worst combo to apply in the same routine. The fix: BP in the AM (or as a short-contact wash), retinoid in the PM. Never layer them. Never mix them. Never apply them on the same half of the day. BP and retinol cancel each other and inflame your skin for free.

Combo: Peptides + Acids (Sensitivity Watch)

Direct acids (AHAs, BHAs) at low pH can hydrolyze peptides, breaking their amino acid chains before they can signal the skin. The data isn't definitive, but the mechanism is plausible. The conservative approach: separate peptides and direct acids into different routines. If you're paying for peptides, don't gamble them against a low-pH toner.

Sunscreen: The Non-Negotiable Layer

Every exfoliant, retinoid, and brightening active increases photosensitivity, making daily broad-spectrum SPF 30+ non-negotiable. Sunscreen isn't optional with actives. It's the deal. You don't get to exfoliate, resurface, and brighten without also committing to UV protection. Using actives without SPF is like sanding your floors and walking on them with muddy boots.

Layering actives is like cooking with heat. You can use low heat on everything and get a gentle, all-day simmer. Or you can blast one pan on high and another on medium and call it a stir-fry. Most people burn the kitchen down because they turned every burner to high at the same time. One active per routine is the low-heat approach that actually works.

Safety & Tolerability: What Can Go Wrong And How To Avoid It

Skincare actives carry irritation potential that scales with concentration, pH, frequency, and skin barrier status. The difference between results and regret is almost always about pacing and patch testing. Start low, go slow, patch test, and use SPF. That's the whole safety playbook.

Patch Testing: The 72-Hour Rule

Apply a pea-sized amount to a small patch (jawline, behind the ear, inner forearm) once daily for 72 hours before full-face use. Watch for redness, stinging, itching, or bumps. A patch test catches immediate irritant reactions, not cumulative sensitivity. Passing a patch test means you can start slowly. It doesn't mean you can go fast.

Purging vs. Breakout: How To Tell The Difference

Purging (from retinoids, AHAs, BHAs, azelaic acid, benzoyl peroxide) produces small, uniform whiteheads or blackheads in areas where you normally break out, and resolves within 4-6 weeks. A true breakout from product incompatibility appears in unusual areas, with varied lesion types, and doesn't resolve until you stop the product. Purging is acceleration. Breaking out is aggravation. Location tells you which is which.

Over-Exfoliation: The Barrier Destruction Spiral

Over-exfoliation presents as tightness, shininess, stinging with neutral products, increased sensitivity, and paradoxical breakouts. The fix: stop all actives, strip the routine to cleanser, moisturizer, SPF only, and rebuild the barrier over 2-4 weeks before reintroducing one active at a lower frequency. Over-exfoliation is the most common self-inflicted skincare injury. It's also the most avoidable.

Photosensitivity: The Cumulative Risk

AHAs, retinoids, and benzoyl peroxide increase UV sensitivity by thinning the stratum corneum or accelerating cell turnover, exposing fresher, more vulnerable cells. This photosensitivity persists for days after application and accumulates with frequency. Daily SPF 30+ is the minimum. Water-resistant SPF 50+ if you're outdoors. Photosensitivity doesn't clock out when you wash your face.

Contraindications & Special Considerations

Certain actives carry documented contraindications: retinoids and high-dose salicylic acid are not recommended during pregnancy or breastfeeding. Benzoyl peroxide can bleach fabrics, towels, and pillowcases. AHAs can increase sensitivity to other actives for 24+ hours post-application. Anyone with a diagnosed medical skin condition should consult their healthcare provider before introducing actives. This is a reference page, not a prescription. We compare published specifications. We don't treat or diagnose.

Skin-Type Mapping: Which Actives Match Which Skin

The right active for your skin type is the one whose mechanism of action matches your primary skin concern at a concentration and pH your barrier can tolerate. Skin type is a starting point, not a fixed category. It shifts with seasons, hormones, age, and your current barrier health. Match actives to your skin's current state, not the state on your driver's license.

Skincare Actives Concentration Chart: The Published Ranges

This is a reference table of published effective concentration ranges for OTC skincare actives, compiled from formulator guidance and ingredient supplier data. These are not our measurements or recommendations. They're the ranges the cosmetic chemistry literature identifies as effective. Check your product label against this chart. If the percentage isn't listed, it's probably below the effective floor.

A critical note on concentration labeling: many products list a blend or complex percentage rather than the pure active percentage. A product labeled "10% glycolic complex" may contain 4% actual glycolic acid plus buffers and botanical extracts. The only number that matters is the free acid concentration at the working pH. Read the full ingredient list. The active's position in the INCI list tells you more than the front-of-bottle marketing number.

Skincare Actives FAQ

What are skincare actives for beginners?

Start with one active at a low concentration: niacinamide 5% (barrier support, minimal irritation), low-percentage lactic acid (gentle exfoliation), or a vitamin C derivative (stable, non-irritating antioxidant). Use it 2-3 times per week, always with SPF in the AM. One active. Low strength. Slow ramp. SPF. That's the entire beginner blueprint. Read more about building a routine at our best budget skincare routine guide.

Which skincare actives are best for acne?

Salicylic acid (0.5-2%) for pore-clearing, benzoyl peroxide (2.5-5%) for antibacterial action, azelaic acid (10%) for combo antibacterial and anti-inflammatory effects, and retinoids (adapalene 0.1% OTC) for cell turnover. Never apply BP and retinoids in the same routine. Split them AM/PM.

Which skincare actives are best for anti-aging?

Retinoids (retinol 0.3-0.5% or retinaldehyde 0.05-0.1%) for collagen stimulation, vitamin C (L-ascorbic acid 15%) for collagen support and photoprotection, peptides for collagen signaling, and AHAs (glycolic or lactic at moderate %) for surface renewal. Retinoids do the heavy lifting. Everything else supports.

Which skincare actives are safe for sensitive skin?

PHAs (gluconolactone), mandelic acid, azelaic acid, niacinamide (2-5%), centella asiatica, panthenol, colloidal oatmeal, and squalane. Avoid glycolic acid, high-percentage L-ascorbic acid, strong retinoids, and benzoyl peroxide. Start with barrier support. Add actives only after the barrier is solid.

What skincare actives should not be mixed?

The documented conflicts: benzoyl peroxide + retinoids (BP oxidizes retinoids on contact), AHAs/BHAs + retinoids in the same routine (irritation overload and potential pH destabilization), and peptides + direct acids (low pH may hydrolyze peptides). Vitamin C + niacinamide is safe with dry-down time between layers, despite persistent myths. See the full breakdown at our layering guide.

What is the correct layering order for skincare actives?

Thinnest to thickest. Water-based before oil-based. Low pH before high pH. Cleanser, toner, water-based actives (vitamin C, BHA, niacinamide serum), oil-based or anhydrous actives, moisturizer, occlusive, SPF (AM). Wait 30-90 seconds between each layer. Wet skin accelerates penetration and irritation. Dry-down time matters.

How do I know if I'm over-exfoliating?

Signs of over-exfoliation: tightness, glassy shininess, stinging with water or neutral moisturizer, increased redness, flaking, and breakouts in unusual areas. Stop all actives immediately. Use only a gentle cleanser, a barrier-repair moisturizer with ceramides, and SPF for 2-4 weeks. Rebuild the barrier before restarting any active at half the previous frequency.

Is purging real? How do I tell the difference?

Purging is real and caused by actives that accelerate cell turnover: retinoids, AHAs, BHAs, azelaic acid, benzoyl peroxide. Purging produces small, uniform whiteheads/blackheads in your usual breakout zones and resolves within 4-6 weeks. A true breakout from product incompatibility appears in unusual areas with varied lesion types and persists until you stop the product. Location and duration are the tells.

Do I need to use sunscreen with skincare actives?

Yes. Non-negotiable. AHAs, BHAs, retinoids, and benzoyl peroxide all increase photosensitivity. Using these actives without daily broad-spectrum SPF 30+ sunscreen is counterproductive and increases the risk of UV damage. No SPF, no actives. That's the deal.