Do oil baths worsen dandruff and seborrheic dermatitis?

Seborrheic dermatitis is a chronic inflammatory skin condition characterized by red patches, greasy scales (similar to dandruff), and itching, primarily located on the scalp, sides of the nose, eyebrows, or behind the ears. This condition is often linked to an overgrowth of a yeast naturally present on the skin: Malassezia .

Although many people use vegetable oils to soothe or moisturize their hair, it is important to know that some oils can, in fact, worsen the symptoms of seborrheic dermatitis and dandruff .

Malassezia yeast and its appetite for certain lipids

The Malassezia yeast, which includes several species such as Malassezia furfur , M. globosa , and M. restricta , is a natural part of the skin microbiome. In some people, this yeast can proliferate excessively, particularly in sebum-rich areas, triggering an inflammatory reaction.

This fungus is distinguished by a particular characteristic: it is lipophilic , meaning it needs lipids (fats) to grow. More precisely, it feeds on fatty acids with a carbon chain length of C12 to C24 , which corresponds to fatty acids whose carbon chain contains between 12 and 24 carbon atoms.

For example :

• Lauric acid has 12 carbon atoms (C12),

• Oleic acid , which is very present in olive oil, has 18 atoms (C18),

• Arachidic acid contains 20 atoms (C20).

These fatty acids are very present in many vegetable oils commonly used in cosmetic care.

How Malassezia digests oils: the role of lipases and phospholipases

Malassezia cannot metabolize complex fats directly. It uses specific enzymes for this purpose: lipases and phospholipases .

• Lipases are enzymes capable of breaking down triglycerides (the main type of fat in oils) into free fatty acids .

• Phospholipases act in a similar way but on phospholipids , essential components of cell membranes.

Once released, free C12 to C24 fatty acids become an ideal fuel source for yeast, promoting its proliferation. This process is often accompanied by the production of inflammatory compounds, which irritate the skin and cause the characteristic symptoms of seborrheic dermatitis: redness, greasy scales, and itching.

The most problematic oils in cases of seborrheic dermatitis

Many natural oils, while popular for their moisturizing or soothing properties, are actually very rich in long-chain fatty acids (C12 to C24). Here are some examples of oils often used in hair or skin care that can nourish Malassezia:

Coconut oil , in particular, is an interesting case. It is often praised for its antimicrobial properties, notably due to caprylic acid (C8), a short-chain fatty acid with antifungal effects. However, it contains approximately 47% lauric acid (C12) , which is highly attractive to Malassezia . Thus, instead of inhibiting the yeast, it can paradoxically promote its growth if used for extended periods on skin prone to dermatitis.

The role of pH and other factors that promote yeast growth

The growth of Malassezia is not only influenced by lipids. The skin's pH also plays a key role.

• A slightly acidic pH (around 4.5 to 5.5) is unfavorable to Malassezia.

• A more neutral or alkaline pH (above 5.5) facilitates the enzymatic activity of yeast and the release of fungal allergens.

In addition, the presence of certain vitamins (B1, B6) or amino acids (such as glycine and asparagine) can also stimulate fungal growth in the presence of an abundance of lipids on the skin.

Recommendations for hair and scalp care

1. Avoid oil baths in case of dandruff or seborrheic dermatitis : classic vegetable oils (coconut, olive, jojoba, argan…), esters, fatty alcohols, polysorbates, long chain ceramides.

2. Favor formulations with an acidic pH (4.5 – 5.5) and no fragrance.

3. Target products that respect the scalp microbiota : Prebiotics, probiotics

Which oil alternatives are safe?

Fortunately, there are alternatives that don't feed Malassezia. Here are three types of oils generally considered safe for skin prone to seborrheic dermatitis :

1. MCT Oil (Medium Chain Triglycerides)

MCT (Medium Chain Triglyceride) oils are composed of short-chain fatty acids, primarily C8 (caprylic acid) and C10 (capric acid) . These fatty acids are not usable by Malassezia , making them ideal as moisturizers.

2. Squalane

Squalane is a stable, hydrogenated form of squalene, a molecule naturally present in human sebum. It is non-comedogenic , non-nutritive to yeast , and offers excellent skin tolerance .

Conclusion

Certain oils, particularly those rich in long-chain fatty acids (C12 to C24) , can unintentionally feed the Malassezia yeast , the main culprit behind seborrheic dermatitis. This biological process relies on the action of lipases and phospholipases , which release free fatty acids from lipids applied to the skin. These fatty acids then become an ideal substrate for yeast growth, exacerbating redness, scaling, and itching.

For those prone to dandruff or seborrheic dermatitis, it is therefore essential to avoid oil baths and use suitable skincare products free of C12–C24 rich oils. A better understanding of ingredients allows you to adopt a more skin-friendly routine and better manage this chronic condition.

https://pmc.ncbi.nlm.nih.gov/articles/PMC7098993/

https://pubmed.ncbi.nlm.nih.gov/35642120/