One conversion step from retinoic acid, so more potent than retinol. In a trial it reduced wrinkles about as well as tretinoin, with less irritation.
Retinaldehyde sits between retinol and retinoic acid in the skin's vitamin A pathway, so it needs only one step to become active. In a randomized trial, 0.05% retinaldehyde and 0.05% prescription retinoic acid both reduced wrinkles over 18 weeks compared with vehicle, and retinaldehyde caused less irritation.
It is less common than retinol because it is harder to stabilize, and product strengths (usually 0.05-0.1%) are often not shown.
A randomized trial of 125 people with sun-damaged skin found 0.05% retinaldehyde and 0.05% retinoic acid both reduced wrinkles and roughness at 18 weeks versus vehicle, with retinaldehyde better tolerated. Earlier work showed dose-dependent retinoid activity in human skin at 0.05-0.5%. The evidence base is small.
125 people with photodamaged faces used 0.05% retinaldehyde, 0.05% retinoic acid or vehicle; both actives reduced wrinkle and roughness measures at 18 weeks, and retinaldehyde was better tolerated.
Retinaldehyde at 0.05-0.5% produced dose-dependent retinoid effects in human skin, such as a thicker epidermis and more cell turnover; in 229 patients, 0.05% and 0.1% preparations were well tolerated on the face for up to 3 years.
Across 654 pregnancies exposed to topical retinoids in the first trimester and 1,375 unexposed, there was no significant rise in major birth defects, miscarriage, low birthweight or prematurity; the authors call this reassuring after accidental exposure but too limited to justify using retinoids in pregnancy.