The most common cause of infectious acne is a fungus called Malassezia (formerly known as Pityrosporum). Malassezia occurs naturally on the skin of humans and many animals. Nearly everyone carries Malassezia on the skin, and it causes no problems for the vast majority of people.

While the data on acne patients is still sparse, a handful of Japanese studies has linked the fungi on acne severity. For example, this 2015 study found that the number of Malassezia correlates better with acne severity than the number of P. Acnes bacteria (the bacterium traditionally linked to acne).

The fungi use lipases (fat digesting enzymes) to break sebum down to glycerol and free fatty acids (FFAs). FFAs have been shown to irritate the skin and increase keratin production, leading to blocked pores. Malassezia itself can trigger inflammation in the skin pores.

Malassezia spp. produce many enzymes (including lipases and phospholipases) that can initiate an inflammatory response by releasing unsaturated free fatty acids from the sebum lipids.

Prohic, A., Jovovic Sadikovic, T., Krupalija-Fazlic, M. & Kuskunovic-Vlahovljak, S. Malassezia species in healthy skin and in dermatological conditions. Int. J. Dermatol. (2015). https://www.ncbi.nlm.nih.gov/pubmed/26710919

All this is to say that Malassezia has the potential to trigger acne, or skin problems often mistaken for acne.

How to tell if you have infectious acne?

The only definitive way is to ask a dermatologist to check what microorganisms inhibit the skin pores. Aside from that, here are some clues that suggest your acne could be caused by Malassezia:

• It gets worse with antibiotics. The bacteria and fungi on the skin compete for living space and nutrients. Antibiotics kill bacteria and allow the fungi to thrive.
• It gets worse in summer and while sweating. Both hot temperature and substances in sweat help the fungi to grow, which is why Malassezia-related skin problems are more prevalent in hot climates. Furthermore, high ambient temperature increases sebum production, which further encourages the fungi growth.
• Pimples look slightly different. Dr. Cynthia Bailey says that: “The pimples of pityrosporum folliculitis are slightly different from those of acne vulgaris in that they are usually bright red and both itch and hurt. Acne vulgaris pimples are typically a deeper purple red and my patients usually describe them as painful, but not itchy. Pityrosporum folliculitis pimples heal differently too, often leaving a brown color along with the red scar. Along with the pimples, there are usually many blackheads and tiny pimple-like bumps that are closed-over blackheads. Some people have just a few lesions, others have thousands.”
• Location. Pimples caused by the fungi are usually worst on the forehead, along the hairline and jawline. Aside from the face, the fungi can cause problems on the neck and back all the way down to the waist.

Treatment

Prevention is the best cure. Here are simple things you can do to prevent the fungi from taking over your skin.

• Wash off sweat as soon as possible.
• Keep the pores open using salicylic acid or retinol. AHAs probably don’t work as well as they are water-soluble and cannot penetrate into fat-clogged skin pores.
• Avoid soaps that increase the skin pH as the fungi grow more slowly in an acidic environment.
• Don’t use antibiotics, topical or oral – unless absolutely necessary.

As to getting rid of existing infections:

• Tea tree oil (TTO). In test tube studies TTO kills the fungi almost as effectively as many prescription antifungals. A study showed that 5% TTO shampoo effectively treated dandruff (also caused by Malassezia fungi).
• Zinc.
• Ketoconazole. The active ingredient in many prescription antifungal creams, shampoos, and drugs.
• Topical probiotics. While there’s no scientific data to confirm that topical probiotics work against Malassezia infections, I think there’s a good chance they will. Consider them as the opposite of antibiotics. Antibiotics can make things worse because they kill off the competing bacteria on the skin. It stands to reason that using topical probiotics to add healthy bacteria on the skin would do the opposite.