If you can make a strong frown shape with your lips when you make a sad face, you may have an overactive muscle in the corners of your mouth, which over time can increase the appearance of a miserable expression when at rest. 


Botulinum relaxes a muscle called the depressor anguli oris, which stops that pulling down of the lips, and gives them back a more relaxed, happy appearance. 


This treatment is not suitable for everyone, you will need a thorough assessment by your practitioner.