Brittle nails can be caused by a range of factors, from ageing and medical conditions, to frequent exposure to harsh chemicals and moisture loss. For those whose nails are constantly splitting, peeling or snapping it can be a real frustration, but according to shoppers, a £16 treatment could be the shortcut to stronger, healthier-looking nails in as little as seven days. Beauty fans dealing with everything from post-gel damage to medical-related brittleness are turning to OPI’s cult-favourite