What is actually
in a lash serum

Prostaglandin analogues

Isopropyl cloprostenate, dechloro dihydroxy difluoro ethylcloprostenolamide (the “MDN” on an M2 Beauté box), bimatoprost and their relatives. They are derived from a glaucoma medication that was found to lengthen patients' lashes as a side effect, and they extend the growth phase of the hair follicle directly.

They work — the fastest results in our panel all came from this family, several of them visible by week three. They also carry the documented risks that make this category contentious: darkening of the lid skin, dryness or itching along the lash line, and, rarely and with prolonged use, a permanent change in iris pigmentation. In the UK they are sold as cosmetics, not medicines, which means the labelling is often quieter than the effect deserves.

Our position: we do not exclude them, we cap their formula score, and we label every product that contains one so the choice is yours rather than ours.

Peptides, biotin and panthenol

The other family conditions rather than instructs. Peptide complexes support the follicle and the keratin structure of the hair, biotin feeds it, panthenol and hyaluronic acid hold water in the lash and the surrounding skin. Results arrive later — density around week five, length nearer week ten — and they arrive smaller.

What they buy you is tolerance. In our panel, no peptide-based serum produced a withdrawal for irritation, and the best of them — the serum at the top of this ranking — finished the trial close behind formulas carrying a prostaglandin analogue.

Reading a UK label

• Check the INCI list, not the front of the box. “Advanced complex” and “growth technology” mean nothing; the ingredient list is a legal document.
• Look for anything ending in -prost or -prostenate. That is a prostaglandin analogue whatever the marketing calls it.
• Check the size against the price. A 2 ml tube at £104 and a 5 ml bottle at £120 are not in the same price bracket, whatever the shelf says.
• Check the period-after-opening symbol. Most lash serums are six months once opened; a tube that lasts nine is a tube you should not still be using.

Using one safely

• Apply once a night to clean, dry skin along the upper lash root only — never to the lower lid or the waterline.
• One stroke per eye. More product does not mean more growth; it means more contact with skin that does not need it.
• Remove contact lenses first and leave fifteen minutes before putting them back in.
• Stop at the first sign of persistent redness, itching or dryness and speak to a pharmacist.
• If you have glaucoma or ocular hypertension, take eye-pressure medication, or are pregnant or breastfeeding, get medical advice before starting anything in this category.

This page is general information, not medical advice. Anything affecting your eyes is worth a conversation with a pharmacist, optometrist or GP.