Smiling can have hidden meanings and act as a mask for those experiencing depression or other mental health issues. While smiling may boost mood through the release of "neuropeptides", it is not always an accurate sign of happiness. Nineteenth century French doctor Duchenne De Boulogne identified 19 different types of smiles related to emotions like joy, aggression, and contempt. Recent studies show that over 70% of young adults in the UK experience stress-related issues like depression. Improving mental wellbeing may involve connecting with others, being physically active, taking notice of one's surroundings, learning new things, and helping others through acts of kindness.