How is this different from a brow pencil, tinted gel or a wash-off tint — and how long does the colour last?

Pencils, powders and tinted gels are makeup: the pigment sits on top of the hairs and skin and comes off when you cleanse your face. This product works differently. It is a two-part oxidative colour system — a colour cream and a developer mixed just before use. The developer allows the dye precursors to form larger colour molecules on the surface of the hair and inside the hair shaft, so the colour becomes part of the hair rather than a coating on it.

In practice, this means:

• It survives daily life. Washing your face, swimming, rain, sweat and rubbing your eyes do not remove the colour the way they would with makeup.
• It fades gradually rather than washing off. As with any hair tinting, the result softens over time as the colour fades slightly and the tinted hairs are naturally replaced by new growth. Brow and lash hairs have a short growth cycle, so most people find the effect noticeable for a few weeks before they consider repeating.
• It does not add volume or new hairs. The dye darkens the hairs you already have, including fine, pale ones that were previously invisible — which is why brows often look fuller afterwards. It does not thicken hairs or change how they grow.

Frequent face oil use, exfoliating skincare applied over the brows, and sun exposure can speed up fading, so keeping active skincare off the brow area helps the result last.