By: Alexandra Tunell

Note from Dr Glow Girl: Interesting that Cellular Skin Rx uses each of these vitamins in our excellent, effective product formulations.

Vitamin A, aka The Anti-Ager

What it is: Vitamin A in its most powerful form is known as tretinoin (Retin-A which is still a prescription cream in the US). The less potent forms of vitamin A are retinol and retinyl palmitate. Neither can be accessed by the skin. They must be broken down into retinoic acid (tretinoin) to be used. Vitamin A stimulates collagen and fibroblast production, resurfaces the skin and softens lines and wrinkles. It is the most powerful topical available.

Who should use it: Start in your mid-30s. If possible, skip the nonprescription tretinoin derivatives and go straight for tretinoin (Retin-A, Renova, Micro-Retin-A). See here for how to incorporate tretinoin into your Cellular Skin Rx routine.

Vitamin B3, aka The Hydrator and Redness-Reducer

What it is: Also known as niacinamide, vitamin B3 boosts ceramide production and strengthens the skin’s barrier function, which is key for locking in moisture and keeping irritants and pollutants out. “Also, it has been known to help with post-inflammatory hyperpigmentation, particularly from acne, by evening out the skin tone,” says Dr. Renee Rouleau.

Who should use it: Anyone who has rosacea or dry, sensitive skin will benefit from B3, though Rouleau says the skin’s moisture barrier typically starts to weaken in your 30s and 40s.

Vitamin C, aka The Brightener

What it is: A topical antioxidant that’s been proven to be highly effective at inhibiting free radicals that cause wrinkles, sagging and general aging. Critical for collagen production. Human skin cannot form collagen without having l-ascorbic acid present.

Who should use it: Anyone, every day, under sunscreen.

Our pick: Cellular Skin Rx, Vitamin C+Firming Serum, $39, www.CellularSkinRx.com

Vitamin E, aka The Reparative Moisturizer

What it is: Vitamin E is an antioxidant that reduces the formation of free radicals and helps to strengthen the skin’s moisture barrier, which is why you’ll find it in after-sun products and treatments for stretch marks and scars.

Who should use it: “Generally, less than 1% should be fine for any type of skin,” says Rouleau.