Bacteria in acne

Although, acne is not an infectious disease, the role of bacteria in acne remains unclear.

At puberty, the number of bacteria on the skin surface increases. These include:

• Proprionibacterium acnes (P. acnes)
• Proprionibacterium granulosum
• Staphylococcus epidermidis

The number of Malassezia yeasts probably also increases.

Severity of acne however does not depend on the number of bacteria on the skin surface or in the sebaceous ducts (the passageway from the oil glands).

The number and activity of P. acnes bacteria varies according to oxygen supply, nutrient supply and pH.

P. acnes can produce active enzymes and inflammatory mediators which may contribute to the activity of acne. These include:

• Lipases
• Proteases
• Hyaluronate lyase
• Phosphatase
• Smooth-muscle contracting substances

The lipases can convert triglyceride in sebum to free fatty acids. The free fatty acids increase clumping of the bacteria and thus colonisation of duct by more of them. The inflammatory mediators penetrate surrounding skin and are a cause of inflammation.