Denatured Alcohol

Denatured alcohol (also known as ethyl alcohol, SD alcohol, or alcohol denat) is a common ingredient in skin care, hair care, makeup and other personal care products.

What is denatured alcohol used for? It acts as a solvent, helping to dissolve other ingredients and creates non-greasy, quick-drying, lightweight formulas that many people (especially those with oily skin) prefer. However, there’s a catch: long-term use of denatured alcohol in cosmetics can cause skin problems under certain conditions. Let’s explore why.

Denatured alcohol becomes problematic for skin when used in concentrations of 10% or greater (typically listed as the fifth ingredient or higher on a cosmetic ingredient list). When used in this high of concentration, denatured alcohol does more than just dehydrate skin—it can irritate skin, weaken its barrier, and even trigger cell death. This is particularly concerning when combined with other irritants often found in personal care products, like menthol or fragrance/essential oils.

The information above pertains to in vivo (on human skin) data; in vitro (petri dish) studies looking at the impact of this type of alcohol on isolated skin cells has shown that small amounts—as low as 3.1%—can cause a statistically significant increase in apoptosis (cell death) within 24 hours of exposure.

Uses of denatured alcohol include in over-the-counter products, in skin care products (including denatured alcohol in sunscreen), and in makeup and fragrances (i.e. perfumes). The level of usage can be as high as 75%. Amounts lower than this are used based on formulation needs around aesthetics and absorbency. Denatured alcohol can be used as a solvent and to improve the texture of fluid/gel formulas. While denatured alcohol can be beneficial for enhancing the penetration of other ingredients into skin, the downsides outweigh the benefits if included in high concentration. There are other types of ingredients (specifically glycols) that can step in to function as solvents and penetration enhancers, although their aesthetics may differ from the “invisible” finish alcohol leaves behind.

Hand sanitizers regulated by the U.S. FDA contain 60-80% alcohol.

Also worth noting: Alcohol concentrations of 10% or more can cause the formulation to be designated as “flammable.”

Denatured alcohol may be sourced synthetically or derived from agricultural products such as corn. In order to keep people from drinking cosmetic alcohol, a bitter-tasting denaturant is added per government regulations. The “SD” in SD alcohol stands for “specially denatured.”

Denatured alcohol works almost entirely through two physical properties: solvency and volatility. As a small, polar molecule it dissolves materials that refuse to go into water alone - many UV filters, resins, film formers and fragrance oils - which is why it turns up in sunscreens, setting sprays and hairsprays, where a clear, stable, single-phase formula is needed.

Its second property is that it evaporates far faster than water. Applied to skin it flashes off within seconds, taking a little surface warmth with it and leaving behind whatever was dissolved in it as a thin, even deposit. That is the source of the cool, weightless, matte finish, and the reason a gel or essence built on alcohol feels lighter than a comparable water-and-glycerin formula. It also means the product sets quickly rather than sitting wet on the surface.

While it is evaporating it is thought to briefly loosen the packing of lipids between the surface skin cells, which is why alcohol-based formulas can carry other ingredients further into the upper layers. That same volatility is why higher-alcohol formulas can leave skin feeling tight: what evaporates is not only the alcohol but some surface moisture with it. Both effects scale with how much is present, which is why concentration, not presence, is the thing to judge.

Denatured alcohol is not automatically a problem. How much is present matters far more than whether it is there at all.

• Read the position, not just the name. Ingredients are listed in descending order down to 1%. Alcohol denat. high up the list points to a meaningful amount; near the end of the list it is a minor solvent you are unlikely to notice. Position is a rough guide only - it depends on what else is in the formula.
• Match it to your skin. Oily and resilient skin often enjoys the fast-drying, matte finish. Dry, mature or easily sensitised skin generally does better with lower-alcohol formulas.
• Mind what you stack. A high-alcohol toner layered under a retinoid or a strong exfoliating acid is more likely to feel uncomfortable than either used alone.
• Follow with something that seals. If you like the texture, apply a moisturiser with glycerin, ceramides or squalane straight afterwards while skin is still slightly damp.
• Give it a fortnight. Tightness, stinging or a rough, flaky finish is your cue to switch to a glycol-based formula instead.