Do oil baths worsen dandruff and seborrheic dermatitis?

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

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

Malassezia yeast and its attraction to certain lipids

The yeast Malassezia, 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, especially 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 develop. Specifically, it feeds on fatty acids with carbon chain lengths from 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, 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 products.

How Malassezia yeast feeds on oils: the role of lipases and phospholipases

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

• Lipases are enzymes capable of breaking down triglycerides (the main type of fat in oils) into free fatty acids.
• Phospholipases act similarly but on phospholipids, essential components of cell membranes.

Once released, free fatty acids of type C12 to C24 become an ideal fuel source for the 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, itching.

The most problematic oils for seborrheic dermatitis

Many vegetable oils, though popular for their 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, but which can nourish Malassezia yeast:

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

This is why our scalp care products are not rich in vegetable oils and do not have an oily texture.

The role of pH and other factors promoting yeast growth

Malassezia growth is not only influenced by lipids. Skin pH also plays a key role.

pH measures the acidity of a substance, and that of the scalp is naturally slightly acidic, around 5. This pH plays a crucial role in protecting the scalp from aggressive agents, helping to eliminate dead cells, and creating an optimal environment for the hair flora to develop.

• 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 the yeast and the release of fungal allergens.

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

When the scalp's pH is unbalanced, the skin barrier becomes more vulnerable, leading to dryness, itching, and increased sensitivity. This is why our products are formulated to respect this natural pH. Thanks to our natural Derma-Probios® complex (Lactobacillus ferments, PHA...), we preserve the balance of the hair microbiome while preserving our products. By protecting the scalp's acid mantle, we help maintain its balance and prevent imbalances, which allows us to avoid certain increasingly controversial preservatives.

Recommendations for hair and scalp care

1. Avoid oil baths if you have 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

What oil alternatives are safe?

There are also alternatives to vegetable oils that are less likely to promote Malassezia proliferation. Here are some types of fats considered safe for skin prone to seborrheic dermatitis:

- Squalane

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

- MCT Oil (Medium Chain Triglycerides)

MCT oils (Medium Chain Triglycerides), often called fractionated coconut oil, are in a neutral, light, and non-greasy form. They consist of short-chain fatty acids, mainly C8 (caprylic acid) and C10 (capric acid). These fatty acids are not usable by Malassezia, making them ideal as nourishing agents.

Conclusion

Certain oils, particularly those rich in long-chain fatty acids (C12 to C24), can unintentionally nourish 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 a perfect substrate for yeast growth, which aggravates redness, scales, and itching.

For people prone to dandruff or seborrheic dermatitis, it is therefore essential to avoid oil baths and to use suitable care products, free of oils rich in C12–C24 fatty acids.

A better understanding of ingredients allows for a more skin-friendly routine and better control of this chronic condition.

Sources:

Saunte DML, Gaitanis G, Hay RJ. Malassezia-Associated Skin Diseases, the Use of Diagnostics and Treatment. Front Cell Infect Microbiol. 2020 Mar 20;10:112. doi: 10.3389/fcimb.2020.00112. PMID: 32266163; PMCID: PMC7098993.

Kumari KMU, Yadav NP, Luqman S. Promising Essential Oils/Plant Extracts in the Prevention and Treatment of Dandruff Pathogenesis. Curr Top Med Chem. 2022;22(13):1104-1133. doi: 10.2174/1568026622666220531120226. PMID: 35642120.