Why it matters: Many common cosmetic ingredients have confusing names but simple functions. Our ingredient decoder breaks down A–Z entries in plain English: What it is → What it does → Who should avoid it → Safe ranges → Works with / Clashes with. We also flag filters like Pregnancy-friendly, Sensitive skin–safe, and Acne-prone friendly so you can quickly find which ingredients suit you. Use this guide to understand your lotions, cleansers, and makeup
Parabens (e.g. methyl-, propyl-, butyl-paraben)
What it is: A family of synthetic preservatives used in cosmetics and body products. Parabens (often listed as -paraben) prevent microbial growth to extend shelf life.
What it does: Stops bacteria and mold from spoiling products. You’ll find them in many makeup, lotion, shampoo, and sunscreen formulas. They’re generally harmless at low levels.
Who should avoid: Mostly people who prefer “paraben-free” for personal or environmental reasons. No scientific link to cancer at cosmetic levels has been found. If you have extremely sensitive skin, patch-test first (rare allergic reactions occur).
Safe ranges: Typically used at low percentages (often <1% each, combined). EU limits total parabens to 0.8% in rinse-off products. In practice, cosmetics are formulated well below any harmful level. FDA reports no evidence of harm from parabens “as used in cosmetics”.
- Works with: Often paired with other preservatives (e.g. phenoxyethanol) for broad protection.
- Clashes with: Parabens are chemically stable; they don’t deactivate other actives.
- Pregnancy-friendly: Yes (FDA finds no proven risk in cosmetics).
- Sensitive skin: Generally okay (non-irritating for most). Test if allergy-prone.
- Acne-prone: Neutral (don’t cause acne, but also no acne-fighting action).
Sulfates (Sodium Lauryl Sulfate / Laureth Sulfate)
What it is: Soap-like detergents (surfactants) that create foamy lather. Common examples are SLS and SLES, derived from sulfuric acid and fatty sources.
What it does: Strongly cleans and foams: it strips oil from skin/hair and helps detergents rinse away dirt. This makes products feel extra “squeaky clean.”
Who should avoid: Sensitive, dry, or eczema-prone skin. Sulfates can irritate eyes and skin and may worsen dryness or acne in reactive individuals. If your skin or scalp is already compromised (rosacea, psoriasis, eczema), sulfate-free formulas are gentler. Sulfates also strip color from hair dye.
Safe ranges: In rinse-off products like shampoos and face washes, concentrations can be high (often 10–25% in shampoos) because they’re washed off. In leave-on items they’re usually <1–2%. There is no systemic toxicity at cosmetic use levels. The main caution is local irritation: prolonged contact at high %, or leaving them on skin, increases risk.
- Works with: Blends well with other milder surfactants (to reduce irritation) and conditioning agents in cleansers.
- Clashes with: Not a reactive ingredient – just avoid combining it with other harsh agents on the same application.
- Pregnancy-friendly: Yes (no known systemic risks from washed-off use).
- Sensitive skin: No – can irritate or dry sensitive skin (use sulfate-free if needed).
- Acne-prone: Mixed – sulfates remove oil (which can help acne), but over-drying can trigger more oil. Rinse thoroughly or choose milder cleansers if breakouts follow.
Mineral Oil (Paraffinum Liquidum / White Mineral Oil)
What it is: A highly refined petroleum-derived oil (sometimes labeled “mineral oil”, “paraffinum”, or “white oil”). It’s the same base material in baby oil and Vaseline.
What it does: An occlusive moisturizer. Mineral oil forms a barrier on the skin to lock in water and soften the surface. It’s an excellent emollient that can soothe and protect very dry skin, diaper rash, or heal minor scrapes by preventing moisture loss.
Who should avoid: Those avoiding petroleum products for personal reasons, or anyone with very oily/acne-prone skin. The American Academy of Dermatology notes people prone to breakouts should skip heavy petroleum products on the face, as they can trap oil. (However, it’s non-comedogenic for most.) Always look for “white mineral oil” or USP-grade on labels to ensure it’s fully refined and free of impurities.
Safe ranges: Used widely – often tens of percent in products like lotions and ointments. In fact, pure mineral oil (petrolatum) can be 80–100% of a formula (e.g. Vaseline is nearly pure). It’s inert on skin and FDA/industry reviews consider it safe if highly refined. Even in baby skincare, it’s common.
- Works with: Compliments humectants (like glycerin, hyaluronic acid) by sealing in hydration.
- Clashes with: Only fabrics – it can stain (oil-based) and may reduce the penetration of water-based actives if used in a thick layer.
- Pregnancy-friendly: Yes (no contraindication; topical use is non-toxic).
- Sensitive skin: Yes (very gentle; rarely causes irritation). Good for eczema/dry skin.
- Acne-prone: Use with caution – avoid heavy facial use if breakouts are an issue.
Retinol (Vitamin A derivatives)
What it is: A vitamin A–derived skincare ingredient (OTC) or retinoid (prescription variants). Retinol comes in creams/serums to improve skin cell turnover and is used for aging and acne. Prescription-strength retinoids (retin-A, tretinoin, etc.) are much stronger; we focus here on topical retinol products.
What it does: Speeds up skin cell renewal. It unclogs pores, reduces fine lines, and boosts collagen production, leading to smoother, plumper skin. It also lightens pigmentation over time. In acne, it prevents dead cells from clogging follicles. In short, it resurfaces dull skin by increasing turnover.
Who should avoid: Pregnant or breastfeeding women (retinoids are teratogenic at high doses). Doctors advise avoiding prescription retinoids during pregnancy and caution with OTC retinol. Otherwise, people with very sensitive or rosacea-prone skin should use it carefully – it can cause redness and peeling during adjustment. Always start slowly.
Safe ranges: Over-the-counter retinol products range from very low (0.01–0.03% as “starter” strengths) to about 1% (the highest OTC). Many daily creams contain ~0.25–0.5%. Studies show even 0.3–0.5% can improve wrinkles, and 0.1% is effective vs. placebo. Dermatologists recommend beginners start at ~0.025–0.03%. Using more (up to 1%) is possible if skin tolerates it. No OTC goes beyond 1% because higher strengths require prescription. Because retinol is light-sensitive, it’s often used at night.
- Works with: Niacinamide and antioxidants (vitamin C) – these can enhance brightening and reduce irritation. Hyaluronic acid or ceramides are great to pair for added hydration. Sunscreen is a must with any retinoid.
- Clashes with: Don’t use retinol with other strong exfoliants at the same time – skip AHAs/BHAs or benzoyl peroxide concurrently to avoid over-irritation. (For example, BP instructions say not to combine with retinoids.)
- Pregnancy-friendly: No (Topical retinoids are generally avoided during pregnancy).
- Sensitive skin: Use with caution (start very low strength). Can cause dryness and redness initially.
- Acne-prone: Yes, very helpful – it’s a first-line acne treatment (keeps pores clear).
Benzoyl Peroxide (BPO)
What it is: A topical antimicrobial medication (often OTC) for acne. It comes in creams, gels, washes, and lotions (2.5%, 5%, 10%, etc.).
What it does: Kills acne-causing bacteria (Propionibacterium acnes) and reduces inflammation. It also helps shed dead skin cells inside pores. The result: reduced pimples (especially inflammatory ones) and prevention of new ones. Unlike salicylic acid, BPO is stronger against bacteria and inflammation, making it excellent for red pustules and cysts.
Who should avoid: Anyone allergic to it or with very dry, sensitive skin. BPO often causes dryness, peeling, or redness, especially at first. Avoid if you have eczema or extremely sensitive areas. (Always do a patch test.) It also bleaches fabrics (clothes, pillowcases) on contact. People prone to dermatitis may choose lower strengths or spot treatments.
Safe ranges: OTC products range from 2.5% to 10% BPO. Lower strength (2.5–5%) is effective for many and gentler on skin; 10% is used for more resistant acne, especially on body. Use as directed (often once daily). Higher strength doesn’t work better for everyone – it just increases irritation. Always rinse thoroughly if using as a wash.
- Works with: Can be combined with topical antibiotics (like clindamycin) in formulations for synergistic effect (killing bacteria via two mechanisms). Also moisturize after BPO to combat dryness.
- Clashes with: Avoid using BPO at the same time as other harsh acne treatments. For example, Cleveland Clinic advises not to use BPO in the same routine as retinoids, salicylic acid, or sulfur products – this can over-dry skin.
- Pregnancy-friendly: Yes (considered safe in pregnancy, since little is absorbed). Use usual precautions (avoid nipple area if nursing).
- Sensitive skin: Use lower % and limit frequency; it can irritate sensitive skin.
- Acne-prone: Yes – one of the best proven OTC acne treatments (especially for inflamed spots).
Fragrance (Perfume/Parfum)
What it is: A complex blend of natural or synthetic aroma chemicals added to products for scent. In the U.S., manufacturers can label all such ingredients simply as “fragrance” on the ingredient list.
What it does: Makes products smell pleasant. It often masks the scent of other ingredients (like some preservatives or botanical extracts). Fragrance can be synthetic or essential oils (rose, citrus, etc.). The formula is proprietary, so you usually won’t see the specific components on the label.
Who should avoid: Anyone with fragrance sensitivity or allergies. Fragrances are a top cause of contact dermatitis – they can trigger itching, redness, or hives in susceptible people. Even “natural” scents (citrus oils, lavender) can irritate or cause allergy in some. If you have eczema, rosacea, or allergic skin, choose fragrance-free products whenever possible. Fragrance can also irritate eyes and respiratory systems in some individuals.
Safe ranges: The exact safe levels aren’t regulated for consumers. Fragrance ingredients are generally used in very small amounts (often <1%). FDA requires overall safety of the formula but does not list thresholds. Allergic reactions can occur even at low levels.
- Works with: Blends with other cosmetic ingredients; stabilizers may be added so the scent lasts.
- Clashes with: Some fragrance components (like citrus oils) can make skin more sensitive to sunlight (phototoxic). Also, fragrance can destabilize vitamin C (ascorbic acid) if mixed improperly.
- Pregnancy-friendly: Generally yes, though strong scents can cause nausea in pregnant people. (Avoid irritating or scented lotions on abdomen if sensitive.)
- Sensitive skin: No – likely irritation. The FDA advises fragrance-sensitive individuals to choose fragrance-free products.
- Acne-prone: Neutral – fragrance itself doesn’t clog pores, but it may aggravate inflammation in acne-prone skin.
Niacinamide (Vitamin B3)
What it is: A form of vitamin B3 (nicotinamide) used in skin care. You’ll see it in serums, moisturizers, and toners.
What it does: A versatile skin conditioner. Niacinamide strengthens the skin barrier by building keratin, leading to smoother, plumper, less irritated skin. It reduces redness and inflammation (helpful in acne, rosacea, eczema). It also regulates oil production and can lighten dark spots and even out tone. In short, it calms and brightens skin. Dermatologists often combine niacinamide with retinol or vitamin C for enhanced benefits.
Who should avoid: Almost no one – it’s well-tolerated by virtually all skin types. Very rarely, someone might experience mild itch or burning, but it’s uncommon. No need to avoid unless allergy (rare).
Safe ranges: Cosmetic formulas typically use 2–5% niacinamide; some products go to 10%. Safety assessments found niacinamide to be non-irritating and non-sensitizing even up to 5–10%. It is considered safe and nontoxic in normal use.
- Works with: Well with other actives – for example, use vitamin C in the morning and niacinamide/retinol at night for complementing effects. It mixes fine with hyaluronic acid, antioxidants, and ceramides. Many products have niacinamide + vitamin C or + hyaluronic for synergy.
- Clashes with: None notable. It’s stable over a wide pH range. In the past there was concern mixing niacinamide with pure vitamin C, but formulations (or separate use times) solve that.
- Pregnancy-friendly: Yes (topical vitamin B3 is safe).
- Sensitive skin: Yes – very soothing. Often recommended for sensitive and acne-prone skin to reduce irritation and redness.
- Acne-prone: Yes – it can help control oil and calm breakouts.
Denatured Alcohol (Alcohol Denat., SD Alcohol)
What it is: Ethanol (the same alcohol in drinks) made unfit for consumption by adding bitter or toxic denaturants. In cosmetics, it’s often listed as “alcohol denat.” or “SD alcohol.” (This is different from fatty alcohols like cetyl alcohol, which are non-drying emollients.)
What it does: A quick-drying solvent or astringent. It evaporates rapidly, which makes products feel lightweight and dry fast. It also “chases” after oil, helping cleansers or toners strip excess sebum. At low levels, it can help ingredients penetrate.
Who should avoid: Dry, sensitive, or compromised skin. Denat. alcohol is known to be very drying: it can disrupt the skin’s natural barrier and cause irritation, redness, or even breakouts. It’s fine in small amounts (to stabilize products), but high up in the ingredient list can spell trouble. If your skin is prone to dryness or if the product has it as one of the first ingredients, consider skipping it.
Safe ranges: In hand sanitizers it’s very high (60–70%), but in cosmetics it’s usually much lower (e.g. 5–20% in toners or perfumed products). At cosmetic levels it’s not “toxic” per se, but dermatologists note it can cause excessive drying and irritation. Fatty alcohols (cetearyl, stearyl) are different – they’re gentle emollients.
- Works with: Often paired with humectants (glycerin, hyaluronic) in formulas to offset dryness. Also used in sunscreens to help them spread easily.
- Clashes with: It can negate moisturizing ingredients if too high, and may inactivate some sensitive vitamins in water-free formulas.
- Pregnancy-friendly: Yes (no toxic risk from the small amounts used on skin).
- Sensitive skin: No – avoid or use formulas buffered with emollients (look for “alcohol denat.” low on the list or not at all).
- Acne-prone: Mixed – it kills acne bacteria but usually very drying. It can worsen acne if it irritates the skin barrier. Some acne toners use it, but often with soothing additives.
Sources: Authoritative dermatology and medical sources, including FDA ingredient guides and healthcare articles
fda.govpubmed.ncbi.nlm.nih.gov
See Also:
Want to put the A–Z into practice? Start with the Ultimate Hair Care Guide for sulfate/silicone basics, then pick a gentle cleanse in Best Shampoo for Fine Hair. For mixing actives safely, see How to Use Estée Lauder Advanced Night Repair. Curious about scent notes vs. “fragrance-free”? Skim Best Feminine Perfume. And for device ingredients’ effect on skin and hair, check Best Home Laser Hair Removal.