What Actually Causes Dandruff?

125 million years ago in China, well-preserved fossils of Sinornithosaurus showed skin cells between feathers and feather parts, identical to human skin cells.

Scientists recognized these skin fragments as dinosaur dandruff, revealing the first known case of this condition.

The skin cell preservation was exceptional, as most dinosaur fossils consist only of bones.

The presence of skin flakes indicates dinosaurs were warm-blooded and had evolved feathers for temperature regulation, placing them physiologically closer to birds and mammals than to reptiles.

Skin cells constantly replenish themselves, with 500 new skin cells created every second.

Cells move through the epidermis, flatten out, and harden before falling off one by one over approximately one month.

Over a lifetime, humans shed about 100 pounds of dead skin, but this typically goes unnoticed because pieces are microscopic.

Dandruff occurs when skin from the scalp comes off in larger visible flakes instead of microscopic pieces, affecting about half of the world's population.

Malassezia globosa is a fungus that lives on the scalp, thriving in the warm moist environment under hair and is thought to be a cause of dandruff.

The fungus is present on everyone's scalp as long as they have hair, yet only half of people develop dandruff symptoms.

Under microscope observation, Malassezia colonies grow close together forming a lawn-like structure similar to grass, and the fungus smells like bread due to its yeast nature.

Malassezia feeds on sebum oils and releases enzymes called lipases that break down fat molecules, producing free fatty acids that irritate the scalp in susceptible individuals.

For some people, the free fatty acids produced by Malassezia are perceived as invaders, triggering the body's defensive forces to attack.

The scalp's defense mechanism speeds up skin cell turnover from approximately one month to as little as seven days, causing cells to shed in clumps of 300-400 together as visible dandruff flakes.

• Dandruff scalps show elevated levels of inflammatory cytokines and histamines which cause itching • Blood proteins appear on the scalp surface, indicating a compromised skin barrier • The skin fails to properly protect against outside irritants

Nearly 4,000 genes are systematically up-regulated or down-regulated in dandruff scalps compared to healthy scalps, including increased immune response genes and decreased lipid metabolism genes.

• Zinc pyrithione • Selenium sulfide • Piroctone olamine

These active ingredients control Malassezia metabolism, suppressing the fungus's bioactivity to reduce irritating substance production on the scalp.

After three weeks of treatment with Head & Shoulders, the gene expression signatures of dandruff scalps revert to healthy patterns, with approximately 3,700 genes flipping from unhealthy to healthy states.

Head & Shoulders reduces Malassezia irritants on the scalp, changes the scalp's inflammatory response, and ultimately reduces visible skin flakes, unlike cosmetic shampoos alone which show no effect on gene expression.