Seborrheic dermatitis (SD) is an inflammatory skin condition that affects some people but not others, even though they may have similar risk factors. We don’t know why this happens but there are some pretty good explanations out there.
Seborrheic dermatitis is not life-threatening, but it can still be distressing, often aggravating depression and stress. There is so much we don’t know about SD. The interplay of factors leading up to it is complex. As an SD sufferer, I spent the first 6 months asking why and experimenting with my lifestyle and diet choices to improve the condition. It took a lot of research, frustration and disappointment before I got to this level of understanding.
For everyone’s sake (any my own), I’m summarising what causes seborrheic dermatitis in this article. I think it’s important we know how and why a disease develops so we can manage it properly.
If you would like to watch the epic explanation of seb derm, complete with barbarians, knights and castles, check out my video. Hope you enjoy watching it as much as I did making it:
If you would rather read, let’s take a deep dive:
Why does seborrheic dermatitis happen?
Seborrheic dermatitis can be triggered by a multitude of factors. In fact, anything and everything can trigger an SD flare. However, these triggers are not the root cause of seborrheic dermatitis. At its heart, seborrheic dermatitis occurs in some people but not in others due to a few major factors occuring at the same time:
- Malassezia yeast overgrowth
- Skin microbiome imbalance
- Sebaceous gland activity and lipid composition
- Impaired skin integrity
- Hyper-reactive immune response to Malassezia byproducts
While seborrheic dermatitis is not a fungal disease, Malassezia yeast plays a major role in the development of SD. Certain skin conditions like increased sebum production and skin microbiome imbalance may lead to an overgrowth of Malassezia.
Malassezia byproducts can infiltrate the skin barrier, leading to an inflammatory response. This inflammation will cause skin barrier dysfunction, allowing Malassezia and its metabolites to penetrate deeper into the skin, resulting in a vicious cycle of inflammation.
Some studies have shown that the levels of Malassezia on SD skin were similar to those found in ‘normal’ people. However, other studies found that higher levels of Malassezia on the skin correlated with increased severity of SD. Still others have found that the number of Malassezia yeast drops with improvement of SD.
Plus, no one can deny that antifungal creams do wonders for SD and in my opinion, is the only topical cream you need to treat SD.
You may be interested in Malassezia and seborrheic dermatitis: Getting to know the yeast.
Skin microbiome imbalance
There is some evidence that certain bacteria contribute to the development of seborrheic dermatitis due to their ability to break down sebum and supply nutrients that encourage Malassezia growth.
Analysis of skin affected by SD showed higher levels of Acinetobacter, Staphylococcus and Streptococcus. Another study reported that Staphylococcus aureus was the most common skin bacteria found on SD patients, suggesting that it plays a role in the disease.
Sebaceous gland activity and lipid composition
It’s not a coincidence that seborrheic dermatitis mostly affects the face, scalp, neck and upper torso. This is because sebaceous glands are found in greatest concentration in these areas.
Sebum is normally produced by the sebaceous glands to keep your skin lubricated and protected from infection. However, when there is high production of sebum, for example, in infants and adolescents or young adults, Malassezia yeast proliferates, increasing your risk for SD.
Sebum production is also influenced by androgens and stress hormones like cortisol. That’s why SD is more common in males, and is often triggered by stress.
The layer of oil on our skin is composed of both sebocyte and keratinocyte derived lipids. Keratinocyte oils are found within the stratum corneum while sebocyte oils are secreted onto the skin surface (sebum).
Malassezia yeast breaks down sebocyte oils, resulting in decreased triglycerides and leaving behind irritating unsaturated fatty acids like oleic acid.
Oleic acid is potentially the main trigger for inflammation in SD. Even when oleic acid is applied topically, patients with SD will experience more symptoms than non-SD patients, displaying their increased sensitivity to the fatty acid.
Further reading: Seborrheic dermatitis: common oils to avoid
Impaired skin integrity
When Malassezia penetrates skin cells, this triggers an inflammatory response in susceptible people. Lots of pro-inflammatory cytokines are pulled to the area. As a result, a red, itchy, sometimes painful rash is formed. The inflammatory response also further disrupts the skin barrier, enabling Malassezia to get deeper in, causing more inflammatory responses.
When you google how to repair skin barrier, most advice centers around topical treatments that contain ceramides, hyaluronic acid and niacimide. These may help in the short term, but longer lasting ‘treatment’ involves dietary and lifestyle changes.
Further reading: Impaired skin barrier in seborrheic dermatitis
Hyper-reactive immune response to Malassezia
Immunosuppression happens all the time for various reasons. A viral illness like COVID, chronic stress, lack of sleep, psychiatric disorders, immune-suppressing drugs, HIV and neurological disorders like Parkinsons can all weaken the immune system. Immune dysregulation contributes to an imbalance in the skin microbiome, allowing Malassezia to multiply.
It is widely accepted that SD occurs due to an abrnomally robust immune response to Malassezia byproducts. However, a small study published in 2002 refutes this, finding no difference in immune response betweeen SD patients, healthy controls, and patients with other inflammatory skin conditions. They suggested SD was more likely caused by direct Malassezia activity like toxin production and lipase activity instead.
However, there is no denying that SD strikes those who have weakened immune systems and also tends to flare when our body’s resilience is low.
Further reading: Is seborrheic dermatitis an autoimmune disease?
To wrap up
While the cause of seborrheic dermatitis is not fully understood, it looks like these 5 factors existing in the same person at the same time feeds into each other, causing a vicious cycle of inflammation.
To treat seborrheic dermatitis effectively and hopefully cure it, we need more than topical creams to kill Malassezia. We also need to treat it from the inside with a healthier diet and lifestyle.
Now that you know the 5 main factors driving seb derm, read How To Prevent Seborrheic Dermatitis