Hair oiling and dandruff: why oil on the scalp may make flakes worse

Oiling your hair makes it slip more easily and cuts down on friction, but if the oil reaches the scalp of someone with dandruff, it may backfire. Malassezia, the yeast linked to dandruff, needs fat to grow, and in the lab it thrives on many oils. A 2023 letter in a dermatology journal therefore recommends that people with seborrhoeic dermatitis oil only the ends of their hair and keep oil off the scalp.

Dandruff vs seborrhoeic dermatitis

Dandruff is flaking of the scalp without inflammation. Seborrhoeic dermatitis is the same process turned up: redness, itch and greasy scale, and it can also appear in other areas rich in oil glands, across the scalp, face and trunk. DermNet puts seborrhoeic dermatitis at about 3-12% of the population, and it tends to come and go.

Known factors include oily skin, stress, lack of sleep and family history, and many people flare in winter.

Malassezia feeds on fat

Malassezia is a group of yeasts that live on normal human skin; about 18 species are currently known. Crucially, they are lipid-dependent: they need fatty acids from outside to grow, so they crowd into oil-rich areas.

DermNet explains that Malassezia’s enzymes break down the triglycerides in sebum into free fatty acids, which may trigger inflammation. Labs even have to add olive oil to the growth medium to culture it.

Having Malassezia on your skin is normal. Problems start when it overgrows and the skin responds with inflammation.

What the 2023 letter says

Mayo, Dinkins and Elewski wrote a letter to the editor of Skin Appendage Disorders (2023, volume 9, issue 2) on hair oils and seborrhoeic dermatitis. The main points:

Point	Detail
Lab result cited	M. furfur grew well on butter, corn oil, olive oil, coconut oil, oleic acid and castor oil, but poorly on a plain sugar medium
Observation	The tradition of oiling the scalp, because flakes are taken for a dry scalp, may make the condition more severe and longer-lasting
Tightly curled hair	Sebum travels down the hair shaft less easily, so more builds up on the scalp; added oil plus infrequent washing may increase the yeast
What oil does well	On the hair shaft, oil reduces friction and may help protect against damage from cleansing agents
Advice	Avoid oil on the scalp; apply it to the ends of the hair instead

The thing to know is that this is an opinion letter with no data from people. The authors themselves say there are no clinical studies on hair oils and seborrhoeic dermatitis and more research is needed. So the evidence is at the level of “a sensible reason for caution”, not “proven”.

Worked example: counting hours of oil on the scalp

Say someone with dandruff oils their whole head, scalp included, with coconut oil and leaves it overnight for 8 hours, 3 nights a week (made-up numbers).

1. Oil sits on the scalp for 8 × 3 = 24 hours a week.
2. Switch to oiling the lengths only. With 30 cm hair, oil the lower 20 cm, starting about 10 cm from the scalp.
3. Oil on the scalp drops to close to 0 hours, and the hair keeps its slip.
4. Wash it out with shampoo, and on dandruff-shampoo days leave the shampoo on the scalp for the time on the label. The AAD notes some need 5-10 minutes.

	Before	After
Where the oil goes	Whole head, scalp included	Lower 20 cm of the hair
Oil on the scalp per week	24 hours	about 0 hours
Slip on the hair	Yes	Yes

Try this for 3-4 weeks and see whether flaking and itch ease. If nothing changes, the oil may not be the problem.

Look after the dandruff too

Keeping oil off the scalp is only part of it. A dandruff shampoo is still the first step. DermNet notes these are usually used twice a week for at least a month. For how often to wash, how to use dandruff shampoo and an example weekly plan, see How to wash your hair right, and when dandruff needs a doctor.

See a dermatologist if:

• dandruff shampoo used as directed doesn’t help
• the scale is thick, red or very itchy, or spreads to the face or body
• you notice patchy hair loss or sores

Scalp flaking can also come from psoriasis, a fungal scalp infection or contact dermatitis, which only a doctor can tell apart.

Common mistakes

Doing this	Why it’s a problem
Seeing flakes, assuming a dry scalp and adding more oil	If it’s dandruff, oil may feed the yeast
Oiling overnight and washing infrequently	Fat sits on the scalp for a long time
Oiling the scalp straight after a dandruff shampoo	You put fat back where you just washed it off
Swapping oils hoping to find one that “doesn’t cause dandruff”	There’s no evidence in people that any oil is safe here
Scratching until the scalp is broken	Risk of a secondary infection

Oil is for the hair, shampoo is for the scalp. If you have dandruff, keep the two apart.

This article is general information, not a diagnosis or treatment.

Sources

• Hair Oils May Worsen Seborrheic Dermatitis in Black Patients — Skin Appendage Disorders 2023 (Karger)
• Seborrhoeic dermatitis — DermNet
• How to treat dandruff — American Academy of Dermatology
• Cutaneous Malassezia: Commensal, Pathogen, or Protector? — Frontiers in Cellular and Infection Microbiology 2020 (PMC)