Hair Care Myths That Dermatologists and Trichologists Commonly Correct

The idea that cutting the ends accelerates growth has no biological basis. Hair grows from follicles beneath the scalp surface at a genetically determined rate — typically around half an inch per month on average, though this varies by individual, health, and age. The ends of your hair are already dead protein; what happens to them cannot signal the follicle to produce more. Regular trims are genuinely useful, but for a different reason: they remove split ends before they travel up the shaft and cause breakage, which helps you retain length rather than generate it faster.

This advice originates from an era before synthetic bristle brushes, when the limited daily brushing of certain hair types did help distribute sebum from root to tip. For most modern hair types — especially chemically treated, fine, or naturally textured hair — 100 strokes of brushing causes far more cuticle abrasion than benefit. Dermatologists generally advise brushing only as needed to detangle, using a wide-tooth comb or a brush appropriate for your hair type, and starting from the ends upward to minimize mechanical stress. See our guide to hair breakage for more on how mechanical damage accumulates.

Hair strands are composed of keratinized (hardened) protein — they have no metabolic activity, no receptors, and no mechanism for adaptation. When a shampoo seems to stop working, the more likely explanations are: seasonal changes in scalp oil production, buildup of silicones or conditioning agents on the strand, or a change in water mineral content. Addressing these requires a targeted fix — a clarifying wash to remove buildup, for instance — not reflexive rotation through different formulas. Switching shampoos frequently without cause can actually disrupt scalp balance.

Research published in hair science literature has found that hair left wet for extended periods undergoes repeated swelling and contraction of the cortex, which may contribute to structural weakening over time. A blow-dryer used on a low-to-medium heat setting, kept moving and held at a reasonable distance, with a quality heat protectant applied beforehand, can actually produce less cumulative damage than air-drying for hours. The relevant variables are temperature, distance, and movement — not simply whether heat is involved. For a thorough look at what heat tools do structurally, see our guide to heat styling and strand damage.

Sebum is a waxy lipid mixture produced by the sebaceous glands attached to each follicle. Its primary roles involve scalp protection and providing a degree of water-resistant coating on the hair shaft. Internal hair hydration — the water content within the cortex that gives hair its elasticity — is a separate matter governed by the condition of the cuticle layer and exposure to humectants. Someone with an oily scalp who washes infrequently can simultaneously have hair that is brittle and moisture-depleted at the strand level. Evaluating your scalp and your hair strands as separate systems leads to more accurate product choices. Our deep conditioning guide covers how to address internal moisture effectively.

Telogen effluvium is a well-documented condition in which a large proportion of hair follicles shift prematurely into the resting (telogen) phase following a significant stressor — which may be physical (surgery, illness, rapid weight loss, childbirth) or severe psychological stress. Shedding typically becomes noticeable two to four months after the triggering event, which often causes confusion about the cause. The condition is generally self-limiting once the stressor resolves, but persistent or severe shedding warrants evaluation by a dermatologist to rule out other causes. This is distinct from androgenetic (pattern) hair loss, which follows different mechanisms entirely.