Some skincare ingredients are worth steering clear of, either because they irritate skin, disrupt your skin’s protective barrier, trigger allergic reactions, or pose safety concerns during pregnancy. The tricky part is that many of these ingredients hide behind unfamiliar chemical names on labels. Here’s what to watch for and why it matters.
Harsh Sulfates That Strip Your Skin
Sodium lauryl sulfate (SLS) is one of the most common cleansing agents in face washes, body washes, and foaming cleansers. It’s effective at cutting through oil, but it does so aggressively. SLS damages the skin barrier, the outermost layer that keeps moisture in and irritants out. Studies measuring water loss through the skin show that SLS exposure leads to measurably higher evaporation, meaning your skin dries out faster and takes longer to recover. In one study, volunteers needed two weeks of twice-daily treatment with barrier-repairing ingredients just to undo the damage from SLS exposure.
Sodium laureth sulfate (SLES) is a milder cousin that goes through extra processing to reduce irritation, but it can still be problematic for sensitive or dry skin. If your cleanser leaves your face feeling tight or squeaky, a sulfate-based surfactant is likely the reason. Look for sulfate-free formulas, especially if you deal with eczema, rosacea, or chronically dry skin.
Fragrance: The Most Common Allergen
Fragrance is listed as a single word on ingredient labels, but it can represent dozens of individual chemicals that manufacturers aren’t required to disclose. Between 1% and 3% of the general population is sensitized to fragrance allergens, and rates are much higher among people already being evaluated for skin reactions. Once you develop a fragrance allergy, it’s permanent.
The most problematic fragrance chemicals include limonene and linalool (common in citrus and floral scents), which form allergy-triggering compounds as they oxidize over time. Balsam of Peru, a natural resin found in many “botanical” products, causes sensitization in roughly 4% to 8% of dermatology patients tested in Europe. A synthetic fragrance ingredient called HICC (sometimes listed as Lyral) became so problematic that sensitization rates reached nearly 20% among tested patients in parts of central Europe before regulators moved to restrict it.
Products labeled “unscented” aren’t always fragrance-free. Some use masking fragrances to neutralize the smell of other ingredients. Look specifically for “fragrance-free” on the label, and scan the ingredient list for the word “parfum,” which is the international labeling term for fragrance.
Formaldehyde-Releasing Preservatives
Formaldehyde itself is rarely added directly to skincare anymore, but several preservatives work by slowly releasing small amounts of it over time to prevent bacterial growth. These releasers are a known cause of contact dermatitis and are among the most frequently flagged allergens in patch testing.
The names to look for on labels include:
- DMDM hydantoin
- Imidazolidinyl urea
- Diazolidinyl urea
- Quaternium-15
- Dimethylhydantoin formaldehyde (DMHF)
These ingredients are still legal in many countries, but they’ve been increasingly phased out by brands responding to consumer demand. If you notice a product causes redness, itching, or a rash that develops a day or two after application (rather than immediately), a formaldehyde releaser could be responsible.
Retinoids and Hydroquinone During Pregnancy
Two ingredients require extra caution if you’re pregnant or planning to become pregnant. Topical retinoids, including tretinoin (prescription) and retinol (over the counter), are forms of vitamin A that speed cell turnover. While only a small amount is absorbed through the skin, four published case reports have documented birth defects consistent with retinoid exposure. The pattern of those defects matches what’s seen with oral retinoid medications, which are firmly established as harmful to a developing fetus. Until larger studies can confirm safety, the recommendation is to avoid topical retinoids entirely during pregnancy.
Hydroquinone, a skin-lightening agent used for dark spots and melasma, has a much higher absorption rate than most topical ingredients. An estimated 35% to 45% of what you apply is absorbed into the bloodstream. Only one small study has looked at hydroquinone use during pregnancy, and while it didn’t find increased risk, the sample size was too small to draw firm conclusions. The high systemic absorption alone is reason enough to minimize use during pregnancy. Most other common skincare ingredients act locally on the skin and produce minimal levels in the body.
Certain Cyclic Silicones
Silicones as a category aren’t inherently harmful to skin. They create a smooth, silky feel and help products spread evenly. But three specific cyclic silicones, known as D4, D5, and D6 (cyclotetrasiloxane, cyclopentasiloxane, and cyclohexasiloxane), raise serious environmental concerns.
The European Chemicals Agency has classified all three as very persistent and very bioaccumulative, meaning they don’t break down easily and they accumulate in plants, animals, soil, and water. D4 is very toxic to aquatic life with long-lasting effects and is suspected of damaging fertility. These chemicals have been detected in remote regions including the Arctic, carried there by long-range environmental transport.
The EU adopted a restriction in May 2024 that covers leave-on cosmetic products like moisturizers, makeup, and hair styling products, expected to reduce emissions of these substances by up to 90% once it takes effect in 2026. If environmental impact matters to you, check ingredient lists for cyclomethicone, cyclopentasiloxane, or cyclotetrasiloxane. Dimethicone, a linear silicone, doesn’t carry the same concerns.
Pore-Clogging Oils and Butters
If you’re prone to breakouts, the oils and butters in your products matter. Dermatologists use a comedogenic scale from 0 (won’t clog pores) to 5 (highly likely to clog pores) to rate ingredients. Anything rated 3 or above is worth avoiding on acne-prone skin.
Common offenders include coconut oil (rated 4), cocoa butter (rated 4), and wheat germ oil (rated 5, the highest possible score). Avocado oil sits at a 3, making it a moderate risk. These ingredients are popular in “natural” skincare, which is part of why switching to natural products sometimes makes breakouts worse.
Safer alternatives for acne-prone skin include argan oil, hemp seed oil, and sweet almond oil (all rated 0), along with grapeseed oil, rosehip oil, and jojoba oil (all rated 1 to 2). Shea butter ranges from 0 to 2 depending on processing, making it a generally safe option for most skin types.
How to Read an Ingredient Label
Skincare ingredients are listed in descending order of concentration, so the first five or six ingredients make up the bulk of the formula. Anything listed after “fragrance” or “parfum” is typically present at less than 1%. This means an irritating ingredient near the top of the list is a bigger concern than the same ingredient near the bottom.
A few practical tips for label reading: “natural” and “clean” have no regulated definition in most countries, so they don’t guarantee safety. “Dermatologist tested” means a dermatologist looked at the product, not that it passed any specific standard. “Hypoallergenic” has no legal definition in the United States. The ingredient list itself is the only reliable source of information about what’s actually in the product.
When in doubt, cross-reference unfamiliar ingredient names with the categories above. Many of the most problematic ingredients go by technical names that don’t hint at what they actually are. DMDM hydantoin doesn’t sound like formaldehyde, and cyclopentasiloxane doesn’t sound like an environmental pollutant, but that’s exactly what they are.