Researchers at University of California, Los Angeles (UCLA) have managed to identify what exactly causes acne.

The researchers though were unable to find out why some people have higher number of ‘bad’ bacteria strains compared to others. The study has been published in the Journal of Investigative Dermatology.
“We learned that not all acne bacteria trigger pimples — one strain may help keep skin healthy. We hope to apply our findings to develop new strategies that stop blemishes before they start, and enable dermatologists to customize treatment to each patient's unique cocktail of skin bacteria”, lead researcher Dr Huiying Li said.
Source-Medindia