Does Using Retin-A During the Day Damage Skin?

Retin A shold be used at night because the sunlight will "deactivate" it and it will lose its efficacy.  Using it during the day will not harm your skin at all. It just means that the potency is less.  I generally have my patients use it at night and then use a sunscreen during the day because the skin can be very sensitive.

Retinoids are notoriously unstable to light, so you will not get the full benefits. Besides, collagen STIMULATION and REPAIR is best accomplished during the evening rest time. Daytime, it should be anti-oxidants added to your sunscreen to PROTECT from further damage. Your dermatologist can best advise you on your individualized program based on your unique needs. You have done no harm, just not as much good as you would have liked.

Retin A is safe. I tell my patients to use sunscreen SPF 30 and up all the time. Also use moisturizer liberally.