Penetration Enhancer

A penetration enhancer is an ingredient added to help another ingredient travel further into skin than it would on its own. Most of what goes onto skin stays near the surface, held back by the stratum corneum, and for some actives that is the whole problem a formula is trying to solve.

Enhancers work by different routes. Some temporarily loosen the lipid packing between surface cells; some hold water in the outer layer so it swells slightly and becomes more permeable; some simply keep the active dissolved and available instead of crystallising on the skin. Propylene glycol, butylene glycol and various alcohols and esters all get used this way.

The trade-off is the point. Deeper delivery raises the chance of an ingredient doing what it is meant to do, and it raises the chance of irritation in the same movement, because the barrier's job is to be selective.

• An enhanced formula is not automatically stronger, and an unenhanced one is not automatically gentler.
• Nothing on a label states that an ingredient is present for this purpose.
• Introducing an unfamiliar product gradually, on a small area first, remains the practical way to find out how your own skin responds.

Anyone with a compromised barrier or reactive skin has a reason to go slowly with formulas built around strong delivery, and to raise persistent irritation with a dermatologist rather than pushing through it.