Retinaldehyde (Retinal)

Retinaldehyde, often called retinal, is a form of vitamin A that sits one conversion step away from retinoic acid, the active form that directly signals skin cells to behave younger.

Vitamin A in skin follows a ladder: retinyl esters convert to retinol, retinol converts to retinaldehyde, and retinaldehyde converts to retinoic acid. Retinol must climb two rungs to become active, while retinaldehyde needs only one, which is why it tends to work faster and more effectively than retinol at similar strengths.

Skin cells only convert as much as they need, so retinaldehyde is generally gentler than prescription retinoic acid, with less of the heavy peeling and redness that can come with it. Once converted, it helps speed up the shedding of dull surface cells, supports collagen production and helps smooth fine lines, rough texture and uneven tone.

It has also been studied for its effect on acne bacteria, so it can suit breakout prone skin that is also showing early signs of aging. A randomized, split face clinical study found that a retinaldehyde formula measurably improved fine lines and photoaging signs, and a more recent controlled trial found a retinaldehyde serum improved skin texture and visible signs of photoaging over the study period.

Like all vitamin A ingredients, it is sensitive to light and air, so it works best in opaque, airtight packaging and is usually applied at night.