We walk around with a deficiency in Vitamin A in every part of skin that is exposed to light. We need to replenish that Vitamin A every day, otherwise our Vitamin deficit translates into skin damage. It takes 7 days of eating a High Vitamin A diet (cod liver oil, liver etc) to fix 30 minutes of sun exposure - it only takes 3 hours after applying Environ AVST moisturiser.
Vitamin A is derived from multiple sources and is available in varying strengths. Beta-Carotene is the mildest form and as the only plant form of Vitamin A, it is derived from Carrots. Retinyl Acetate and Retinol Palmitate are the most common forms of Vitamin A found in skincare as they are the lowest level of Retinoids, however Retinol is also present in products that contain strong Vitamin A. Retinoic Acid is the strongest, and is rarely used in skincare.
There are other important Vitamins that work well alongside Vitamin A. Vitamin C is essential for the production of collagen and elastin as well as reducing pigmentation blemishes. Vitamin E is an oil phase antioxidant and is essential for the preservation of cell walls.
This photo is an excellent representation of before and after Vitamin A use, and also shows why there is a misconception regarding "thinning" of the skin through Vitamin A use.
In the Epidermal (top) layer of skin, Vitamin A helps to speed up cell renewal (faster healing time), potentiates Langerhans Cells (responsible for skin immunity, hence reducing breakouts), assisting the repair of UV damage as well as compacting the Horny layer and thickening the underneath layer.
In the dermal (bottom) layer of skin, Vitamin A helps to stimulate fibroblasts (thus promoting collagen), stimulates blood vessels (allows more oxygen and nutrients to reach the skin), increases production of moisture retaining cells as well as normalising sebum (oil in the skin).