Causes of Dandruff

Dandruff has one central cause and several accomplices. Understanding them explains why flakes come back every winter and why stress weeks show up on your shoulders.

The central actor: Malassezia

• A yeast that lives harmlessly on every human scalp, feeding on the oils (sebum) your scalp produces
• As it digests those oils it releases oleic acid - and in susceptible people (about half of us) the skin reacts to oleic acid with low-grade inflammation
• The inflamed scalp speeds up skin cell production, and the surplus cells clump with oil and shed as visible flakes
• So dandruff is not the yeast itself but your skin's reaction to it - which is why only some people get it

The accomplices

• Oily scalp: more sebum, more yeast food - dandruff is rare before puberty for exactly this reason
• Infrequent washing: oil and flakes accumulate; regular washing genuinely helps
• Weather: cold, dry winters famously worsen it (dry indoor air plus hat-wearing)
• Stress: a real, documented trigger - flares follow stressful weeks
• Product buildup: heavy styling products, and paradoxically some hair oils - Malassezia feeds on certain oils
• Skin conditions: seborrheic dermatitis, scalp psoriasis and eczema produce bigger, redder flaking
• Rarely: neurological conditions and weakened immunity worsen seborrheic dermatitis

What does NOT cause dandruff

• Dirty hair (though washing helps control it)
• Sharing combs or pillows - it is not infectious
• Hair dye or shampoo "chemicals" - some products irritate, but they do not create dandruff
• Diet alone - no food causes it, though nutrition plays a supporting role

One-line summary

Dandruff is your scalp's inflammatory reaction to a normal oil-eating yeast - amplified by oiliness, winter, stress and infrequent washing, and never caused by dirt or catching it from someone else.