Botox blocks signals from the nerves to the muscles. The injected muscle can't contract. That makes the wrinkles relax and soften. Botox is most often used on forehead lines, crow's feet (lines. Botox (Botulinum toxin) injections relax the muscles in your face to smooth out lines and wrinkles, such as crow's feet and frown lines. It's not permanent – it usually lasts for around 3 or 4 months. In the UK, the cost of Botox injections can vary from about £100 to £350 for each treatment, depending on the clinic and the area being treated.