Bacteria, when caught in certain circumstances such as in a clogged pore, surrounded by oil and no air, can cause the inflammatory response known as acne, a study has found.The propionibacterium acnes -- bacteria known to contribute to acne as well as certain other infections -- usually lives on the skin harmlessly. The study, led by researchers from the University of California, at San Diego, in the US, showed that when trapped in airless environments alongside hair and skin cells, propionibacterium acnes turns serum -- the oil found on our skin -- into fatty acids that activate inflammation in nearby skin cells.Usually this inflammation is switched off by histones -- known as enzymes -- but the fatty acids produced by the bacteria deactivate that brake, so inflammation continues and causes the red, itchy breakouts."Under certain conditions, propionibacterium acnes will secrete fatty acids that inhibit two enzymes in keratinocytes-cells that make up most of the skin's outermost layer. That, in turn, boosts the cells' inflammatory reactions," Richard Gallo from the University of California, San Diego, was quoted as saying to the Health Day.Further, the study may also help explain the process underlying acne and folliculitis -- an inflammation of a hair follicle that causes pimple-like bumps or other skin symptoms.The study was published online in the journal Science Immunology.