You can’t talk about seborrheic dermatitis without also mentioning Malassezia. The two are so intertwined that some people mistakenly believe that seborrheic dermatitis is a fungal infection. SD is a lot more complicated than that but one thing is for sure, Malassezia yeast plays a crucial role in seborrheic dermatitis and treatments aimed at eradicating it are very effective in controlling the disease.
Let’s take a deep dive:
What is Malassezia?
Malassezia is a type of yeast (fungus) that is a part of the normal skin microbiome. They are especially prevalent on the scalp and face because they thrive on lipids (fats).
There are at least 14 species of Malassezia, 8 of which live on people. Malassezia furfur is the most well-known as the causative yeast for seborrheic dermatitis. However, others like M. globosa, M. restricta, M. sympodialis, M. obtuse and M.slooffiae have all been associated with SD.
What does Malassezia feed on?
Malassezia is well-adapted to live on human skin. The fungus needs external fats to grow and use lipase enzymes to process sebum triglycerides. In other words, Malassezia is a yeast that feeds on sebum, the natural oils of our skin.
Even though the various types of Malassezia need a different number and types of lipids to grow, by and large Malassezia feed on long-chain fatty acids (LCFA). That’s why applying plant-based oils that are rich in LCFA aggravates SD. In fact, Malassezia is grown in olive oil cultures in lab studies. Studies also found that almost all Malassezia species required myristic acid to grow. We don’t hear of this saturated fatty acid much but it’s actually found as a minor component in oils like coconut oil, palm kernel oil, and even cow’s milk and breast milk.
That’s why MCT oil is safe in SD but not coconut oil:
Once the LCFAs are taken into the cell, they are activated to long-chain fatty acyl–CoA by various metabolic pathways. One way LCFAs are metabolized is via lipase activity. This enzyme converts neutral lipids like LCFAs to free fatty acids and acylglycerol. Free fatty acids can potentially trigger inflammation of the skin and lab studies actually show that when they stop lipase from functioning, it decreases skin and tissue damage.
What encourages Malassezia growth?
Malassezia is normally found on the skin surface. However, when the skin’s natural balance is disrupted, these yeasts can overgrow and in susceptible individuals like you and me, cause seborrheic dermatitis.
There are so many things that can encourage Malassezia growth, but these are the most common causes:
- Hot, humid weather
- Ironically, dry cold weather as well
- Skin microbiome imbalance
- Applying oils that feed Malassezia to your scalp or face
- Increased sebum production, for example during puberty
- Stress, depression and fatigue
- Chronic illnesses like HIV, Parkinson’s, epilepsy and Hepatitis C
- Medications like lithium, psoralen, chlorpromazine, methyldopa, and the list goes on
- Vitamin and mineral deficiency, especially B vitamins and zinc
- High sugar intake (even though Malassezia doesn’t feed on sugar, it can aggravate SD)
Further reading: What triggers seborrheic dermatitis?
Is seborrheic dermatitis caused by Malassezia?
There is still much to learn about seborrheic dermatitis, but researchers are making progress in understanding this condition. It’s still not clear why some people develop this condition while others do not. However, there are several factors that may play a role and Malassezia is a key player.
Malassezia colonizes our skin almost immediately after birth and is recognized by our immune system as a normal skin inhabitant. However, the same yeast can cause problems when it invades the stratum corneum (the top layer of our skin), triggering our immune system to retaliate.
Malassezia causes inflammation by releasing byproducts like oleic acid, arachidonic acid, malassezin and indole-3-carbaldehyde that is irritating to our skin.
There are 2 main reasons why we think Malassezia is very much involved in seborrheic dermatitis:
- Many studies have found higher levels of Malassezia on skin affected by seborrheic dermatitis
- Antifungal medications are very effective in treating the condition
How does Malassezia affect the skin in seborrheic dermatitis?
Researchers are perplexed as to why Malassezia can affect the skin differently, sometimes even in the same person. For example, Malassezia causes both seborrheic dermatitis and pityriasis versicolor. However, inflammation is characteristic of seborrheic dermatitis but there is no element of inflammation in pityriasis versicolor at all.
Specifically in SD, Malassezia can cause these effects on the skin:
- Malassezia byproducts like oleic acid triggers inflammation, leading to redness, itch, and sometimes even burning.
- Malassezia changes the composition of our natural sebum, which encourages more Malassezia growth
- Inflammation will break down the skin barrier, allowing Malassezia to burrow deeper into the stratum corneum, causing more inflammation
- Even after an SD flare, your skin is dry and sensitive as the skin barrier is damaged.
Don’t you just hate Malassezia and all the trouble it is causing us? If only there was a way to prevent Malassezia from wreaking havoc.
How to prevent Malassezia growth?
Unfortunately, there is no known way to prevent Malassezia growth altogether. And I’m not sure you would want to either. Eradicating Malassezia totally would probably upset the balance of our skin microbiome and who knows what the consequences are.
However, there are plenty of ways we can discourage its growth:
- Using a dehumidifier if you live in hot, humid environments
- Having a shower, washing your face and hair after excessive sweating.
- Getting enough sunlight (but not too much)
- Using moisturizers that hydrate our skin and reduce sebum production
- Using antifungal creams like Lotrimin to kill Malassezia
Further reading: What is the best antifungal cream for seborrheic dermatitis?
You can also strengthen your skin barrier so whatever Malassezia you do have can’t penetrate as deep into the skin:
- Choose moisturizers that contain ceramides, niacimide and hyaluronic acid to protect and repair your skin barrier
- Eating a diet high in whole foods and plants, and low in sugar and processed foods.
- Introduce probiotics into your diet, via food or supplements.
- Stop smoking
- Reduce stress
Further reading: Impaired skin barrier in seborrheic dermatitis
To wrap up
It’s amazing how a small yeast like Malassezia, a normal member of our skin microbiome, can cause so much havoc when it overgrows and penetrates deeper in. However, Malassezia is only one part of the equation that causes seborrheic dermatitis.