3 vitamins that help your skin — and 2 you shouldn't invest in, according to dermatologists

• Insider asked two dermatologists which vitamins you should and shouldn't add to your skincare routine.
• Vitamin A derivatives help clear acne and discoloration, and vitamin C minimizes skin damage.

Vitamins are essential for your body to function — and they can even give your skin an extra boost.

But while some vitamins — A and C, for example — promote skin cell growth, others may not be worth your time and money, and beauty brands might use them as a marketing technique rather than true solution.

Insider spoke to Dr. Afton Cobb, a Jackson Hole-based board-certified dermatologist, and Dr. Hadley King, a New York City-based board-certified dermatologist, to understand which vitamins can help your skin, and which ones to avoid.

Dermatologists recommend using retinoids, derived from vitamin A, to clear acne and discoloration

If there's one vitamin you should buy for your skincare routine, choose vitamin A, Cobb said.

Retinoids are vitamin A-based formulas that can increase skin cell turnover, improve discoloration, and plump the skin — all uses for combating signs of aging.

Vitamin A derived products can minimize acne by reducing skin cells that get clumped up or clogged in pores as they mature through the skin, according to Cobb.

The vitamin can help psoriasis patients with "scaly" skin by thinning out the top skin layer, and it can minimize brown spots and discoloration by inhibiting pigment production.

Vitamins C and E taken together can minimize skin damage

Vitamin C is required in the synthesis of collagen, King said. Collagen is the main protein in the structural and connective tissues in the body, which includes skin, bones, and muscles.

Though oral collagen supplements may not help the skin stay firm and plump as you age, Cobb said topical vitamin C can combat the damage and breakdown of collagen when the skin is exposed to sun, smoking, or pollution.

"Vitamin C in our skin is actually one of the key factors in how collagen is made and stabilized," Cobb said. "The thought is that if you use topical vitamin C, it can help minimize the damage from the environment and the sun to help prevent wrinkles and aging because it can boost collagen."

There are some downsides to using topical vitamin C. One is that many topical formulas are acidic and can irritate the skin, Cobb said.

Vitamin C can also be unstable, or changes form when exposed to light — meaning the product loses its ability to help the skin as soon as it comes out of the bottle. Some research shows combining vitamin C with vitamin E can stabilize the molecule, making the two in tandem more effective than just taking one, King said.

Biotin, a B vitamin, is popular for skin and nails, but it can be risky and pointless

Biotin, also known as vitamin H or vitamin B7, is a water-soluble vitamin found in cooked eggs, salmon, beef liver, and avocados, per the Harvard School of Public Health. The nutrient helps break down fat, carbs, and protein in food and helps in regulating cell signals.

While some supplement sellers tout biotin as the key to healthy skin, hair, and nails, research has yet to bear out this claim. According to Harvard, few published studies suggest biotin supplements can aid in hair and nail growth, and the small studies that appeared to show a benefit did not measure whether participants were deficient in the nutrient.

Cobb said she does not recommend biotin to patients. Biotin can be dangerous, as it can interfere in lab results for troponin, a marker in the body that appears during a heart attack. Biotin skews lab results to show low troponin levels, when the body actually has a lot more of it.

"So if you were having a heart attack and you were taking biotin, then your doctors may not know that you were having the heart attack because the troponin would be falsely low," Cobb said.

Vitamin K is touted for undereye circles, but there's very little evidence for it

Like biotin, vitamin K does not have enough research around its efficacy to make it a reasonable buy. Vitamin K aids in blood clotting, and some people say the nutrient can reduce the appearance of undereye circles by healing broken blood vessels in the area.

But King said there is "not a lot of data" suggesting vitamin K can improve dark circles under the eye. Cobb said vitamin K may help with bruising, but it's not the first thing she would reach for to treat undereye circles.

King said to make sure quality research around topical vitamins exists before purchasing a product, as companies can sometimes use vitamins as a "marketing technique."