Everyone has a certain amount of bacteria living in and on their body. Some species of bacteria are good for the body and help it to stay healthy. Other species can have a negative impact on the body. In acne, the bacteria known as Propionibacterium acnes (or P. acnes for short) can have an effect on the development acne ‘lesions’ (e.g. spots).
P. acnes lives on the skin and is commonly found within hair follicles, where it feeds on dead skin cells and sebum, which is the oil produced by your skin. If a hair follicle becomes blocked, or if the sebaceous gland starts to produce an increased level of sebum, then the conditions become ideal for P. acnes to rapidly multiply.
As P. acnes feeds, it releases substances that help it digest its nutrients. Some of these substances weaken the follicle wall and make it more susceptible to tearing. If the follicle wall splits then white blood cells will rush in to fight the bacteria, which can result in inflammation, redness and pus. The more bacteria that there are, the more white blood cells will arrive to fight it.
It is important to remember that the presence of bacteria on your skin is normal, and the development of acne is not a sign of poor hygiene. It is also important to remember that acne is not contagious. Everybody has a form of P. acnes living in and on their skin; certain strains are just more likely to cause inflammatory acne than others.