The honest truth about hair, skin and nail supplements is that most of them only help if you were short of something in the first place. If your levels are fine, taking more does not push hair growth or skin quality past your normal baseline. The exception worth flagging is biotin, not because it works wonders, but because at high doses it can quietly distort important blood tests.
The biotin trap
Biotin is the headline ingredient in most hair-and-nail supplements, often at very high doses. The catch is that above around 5,000 micrograms it interferes with a wide range of blood tests, including thyroid and heart (troponin) tests, making the results read falsely high or low depending on the test. People have been misdiagnosed off the back of this. There is also little evidence that high-dose biotin helps hair or nails unless you were genuinely deficient, which is rare. If you take a high-dose biotin supplement, stop it for a couple of days before any blood test and tell whoever takes the blood.
The ones that help if you are short
A few nutrients genuinely affect hair and skin when you are low in them. Iron deficiency is a real and common cause of hair shedding, especially in women, which is why a ferritin test is more useful than a hair supplement. Zinc matters for skin and hair, though taking it long-term without copper has its own catch. And vitamin C is needed to make collagen, the protein behind skin structure.
What about collagen?
Collagen supplements have some genuine, if modest, evidence for skin elasticity and hydration, more than most hair-and-nail products can claim. They are reasonably safe and worth a try if skin is the priority, with realistic expectations. For skin, what you put on it (a retinoid, sunscreen) tends to outperform what you swallow.
The honest version
Before buying a hair-and-skin supplement, the higher-value move is a ferritin test, since correcting low iron does more for hair than any dedicated product. To check any supplement against a medication you take, the free checker will show you the result and the reasoning.