Skin supplements: what biotin, zinc and co. actually do, according to studies

ACTIVE INGREDIENTS

Do skin supplements do anything if you are not deficient?

If you are not deficient, the classic skin supplements usually do little that you would notice in the mirror. The reason is a matter of principle: vitamins and trace elements are essential for the skin, but the body needs a certain amount of them, and anything beyond that does not make well-nourished skin any better. A deficiency, on the other hand, often shows in the skin, hair and nails, and that is where topping up genuinely helps. A large part of the advertising relies on exactly this confusion: what works for people with a deficiency is promised to everyone. Things look somewhat different for products that are not aimed at a deficiency at all. A meta-analysis in Frontiers in Nutrition evaluated 66 randomised trials on skin hydration and found effects compared with placebo for collagen, ceramides, hyaluronan and procyanidin, although most of the trials ran for no more than 24 weeks. The classic skin, hair and nail ingredients biotin and zinc do not appear on that list.

So if you are not deficient, your money is better spent in two other places: on daily sun protection and on a pared-back skincare routine that works where you apply it. What a capsule delivers passes from the gut into the bloodstream and is distributed throughout the body. What a serum contains goes straight onto the skin’s surface. That is the approach behind The Duo with its disclosed concentrations: 5% niacinamide, 2% vitamin C as 3-O-Ethyl Ascorbic Acid, 1% zinc PCA, ceramide NP and hyaluronic acid in three molecular sizes. It does not make up for a nutrient deficiency, though – no skincare can. Which factors count outside the bathroom cabinet is covered in the article on what really slows down skin ageing.

What does biotin do for your skin, according to studies?

Studies show a benefit from biotin almost exclusively in people with a deficiency or a specific medical condition, not in healthy skin. In 2017, a review by Patel, Swink and Castelo-Soccio in the journal Skin Appendage Disorders searched systematically for evidence on biotin for hair and nail growth. It found 18 reported cases, and every one of the people involved had an underlying cause for the poor growth. In these people, the condition improved with biotin. The authors see a benefit most likely in acquired or inherited biotin deficiency and in individual conditions such as brittle nails. For healthy people, they consider the evidence insufficient. For the skin itself, the picture is even thinner, because most studies focus on hair and nails.

The fact that biotin is nonetheless found in almost every skin, hair and nail supplement has to do with its reputation and with an authorised health claim relating to the skin, not with a study on healthy skin. On top of that comes a side effect that has nothing to do with the skin at all: larger amounts of biotin can skew lab results, for example thyroid values. What one study found on this is covered below in the frequently asked questions.

What does taking zinc do for your skin, and when is it a matter for your doctor?

Oral zinc has mainly been studied in acne, and acne is a matter for a dermatologist, not for self-experimentation. In 2020, a systematic review and meta-analysis by Yee and colleagues in Dermatologic Therapy found that people with acne had lower zinc levels in their blood on average than control subjects. Treatment with zinc – taken orally in some of the studies analysed and applied to the skin in others – mainly reduced the number of inflamed papules, either on its own or alongside another therapy. That does not mean, however, that zinc tablets make sense for all blemish-prone skin. Acne has several causes, and which treatment is right, zinc included, is something to discuss with your doctor or dermatologist. Dosages from online forums are no substitute for that, especially as high amounts of zinc taken over a long period can affect the absorption of other trace elements.

For skin without acne, there is no evidence of a visible effect from extra zinc. If you are prone to blemishes, skincare for blemish-prone skin is usually the calmer first step: gentle cleansing, few products and patience. Zinc on the skin, by the way, is a different matter from zinc in a tablet – more on that in the frequently asked questions.

Omega-3, vitamin C, vitamin D and co.: what is the evidence for skin?

Omega-3, vitamin C and vitamin D follow the same pattern as biotin and zinc: a deficiency harms the skin, but there is little evidence that extra amounts help skin that is already well supplied. For omega-3 fatty acids, a review by Pilkington and colleagues in Experimental Dermatology describes mechanisms through which they could protect the skin from UV damage, and classes them as a possible additional measure alongside sun protection, not as a replacement for it. The body needs vitamin C to form collagen, and a severe deficiency also shows in the skin. Whether tablets do anything visible on top of a normal diet is far less clear than the role of vitamin C in skincare, which is explained in the article on vitamins in creams and serums. Vitamin D is produced by the skin itself under UV light. As a supplement, it is a matter for your bones and immune system, and a blood test will show whether you need one. Collagen drinks have their own body of research and are a separate topic, distinct from what collagen in a cream can do.

What do claims like ‘contributes to the maintenance of normal skin’ on the packet mean?

The phrase ‘contributes to the maintenance of normal skin’ is an authorised health claim, not a promise of better-looking skin. In Switzerland, as in the EU, wordings like this are set out in a fixed list, and a manufacturer may use them if the product contains a certain minimum amount of the nutrient. What the claim establishes is the nutrient’s role in the body: without it, the skin does not function normally. What it does not establish is that extra amounts make a visible difference to someone who is already well supplied. So the word ‘normal’ is meant literally: it refers to the normal state, not to an improvement beyond it. Claims of this kind exist for biotin, zinc, niacin, riboflavin and vitamin A, among others.

For you, this means that such a claim tells you a nutrient is necessary, not that you need more of it. A supplement with six of these phrases on the packet sounds comprehensive, but it simply proves the same principle six times over. Whether you are low in any of these nutrients is not written on any label.

When is a blood test better than a skin, hair and nail supplement?

A blood test makes more sense as soon as you have a specific concern, rather than simply wanting to do something for your skin. In these cases, it is not about skincare but about finding a cause. That could be a deficiency, but it could also be a thyroid disorder, a skin condition or a side effect of medication. Taking a combination supplement on a hunch tends to cloud this question rather than answer it, and it can skew the lab results you will need later. Which values are worth testing is something your GP decides based on your symptoms. A large panel on your own initiative is rarely necessary. Typical reasons for that conversation include:

• Hair loss that persists for weeks or suddenly gets worse.
• Nails that change, become brittle or discolour.
• Skin that stays noticeably dry, flaky or sore despite good skincare.
• A very unbalanced or severely restricted diet over a longer period.
• Acne or other skin changes that do not settle down over several months.

Frequently asked questions