Written by the Re:Cosm team · Last reviewed September 23, 2026 · Cosmetic information, not medical advice
In short: A water-soluble B vitamin involved in keratin production. In a serum it works as a conditioning ingredient that supports stronger-looking, more resilient lashes.
What it is
Biotin is vitamin B7, a water-soluble vitamin the body uses in several metabolic processes, including the production of keratin, the protein lashes and hair are made of. It is one of the most familiar ingredients in hair care because a real biotin deficiency is associated with hair thinning.
What topical biotin can and cannot do
Here is the honest version. Most people are not deficient in biotin, and there is little evidence that adding more of it, by mouth or on the skin, changes hair in people who already have enough. Biotin in a lash serum is not a growth ingredient.
What it does contribute is conditioning. Biotin is a small molecule that sits comfortably in a water-based formula, and alongside panthenol and hyaluronic acid it is part of a routine that keeps lashes supple and less prone to breaking. Fewer broken lashes is the most realistic route to lashes that look fuller.
Biotin supplements and lash serums
If you take a biotin supplement, a topical serum does not add to or interfere with it. One practical note: high dose biotin supplements can affect some laboratory blood tests, so tell your doctor you take them before bloodwork. Topical biotin at cosmetic levels is not a concern here.
Where it sits in the Re:Cosm formula
Re:Cosm Lash Conditioning Serum has 29 ingredients, and this page covers one part of that formula: a prostaglandin-free, fragrance-free and oil-free peptide serum made in Korea by Kolmar Korea. Every ingredient and the job it does is decoded on the lash serum ingredients guide, and the full label is on the product page.
Common questions
Does biotin in a lash serum make lashes longer?
Not directly. Biotin conditions lashes and supports their structure. Lashes that break less look fuller over time, which is the realistic benefit.
Is biotin safe to use near the eyes?
Yes. Biotin is a vitamin with a long history in eye area and hair products and is well tolerated at cosmetic concentrations.
Should I take biotin supplements for my lashes?
Only if a doctor has identified a deficiency. For most people, supplements are unlikely to change lashes, and high doses can interfere with some blood tests.
Other ingredients in the formula
- Acetyl Tetrapeptide-3 and Capixyl™
- Panthenol
- Hyaluronic Acid (Hydroxypropyl Trimonium Hyaluronate)
- Centella Asiatica, Licorice Root and Houttuynia Cordata
Also worth reading: lash serum ingredients to avoid and what prostaglandin-free means.
Sources and standards
Ingredient facts are checked against our published formula and the sources below. We describe how lashes look and feel, never growth: that is a drug claim, and our serum is a cosmetic.
See the whole formula
Prostaglandin-free. Fragrance-free. Oil-free. Every ingredient published.
View Lash Conditioning Serum