How to wash your hair right, and when dandruff needs a doctor

Washing your hair well comes down to four habits: wash as often as your scalp needs, put shampoo on the scalp, put conditioner on the lengths, and use warm water instead of hot. If you have dandruff, start with a dandruff shampoo used exactly as the label says, and see a dermatologist if it does not improve. This article explains the reason behind each habit and the places people usually go wrong.

Shampoo is for the scalp, not for scrubbing the hair

What actually needs cleaning is on the scalp: oil, shed skin cells and product buildup. The American Academy of Dermatology (AAD) recommends putting shampoo on the scalp rather than working it through the full length of the hair, which only dries the hair out.

How to do it:

1. Wet your scalp and hair all the way through.
2. Spread shampoo between your palms and massage it into the scalp with your fingertips, not your nails.
3. As you rinse, let the water carry the lather down the lengths. That is enough to clean them.
4. Rinse thoroughly, especially at the roots and the nape, so no product is left on the scalp.

How often to wash: look at your own scalp

There is no single right number. The AAD gives guidance by hair and scalp type:

Hair and scalp	Guidance
Straight hair, oily scalp	Washing daily is fine
Dry, curly, thick or tightly coiled hair	Wash as needed, but at least every 2-3 weeks
Flaking	Can come from washing too rarely, or from a conditioner or oil that does not suit your hair

Hot, humid weather and a sweaty day make many people wash more often than someone in a cold climate would, and that is normal. Let your scalp decide: if it feels greasy or smells, wash; if your hair feels dry but your scalp is comfortable, you can skip a day.

Conditioner goes on the lengths

Conditioner reduces friction between hairs, so hair combs more easily and tangles less. Use it after every shampoo, on the lengths and ends rather than the scalp.

• Fine or straight hair: ends only. Taken to the roots it can make hair look flat and greasy.
• Dry or curly hair: the whole length.
• Rinse it out completely, unless the label says it is a leave-in.

Afterwards, wrap your hair in a towel to soak up water instead of rubbing it. Wet hair is more fragile than dry hair. To detangle, use a wide-tooth comb and start at the ends, working up. Let straight hair dry a little before combing; textured or tightly curled hair is easier to comb while still damp.

Warm water, not hot

Your scalp is skin like the rest of your body. For dry skin, the AAD recommends keeping showers to 5-10 minutes and using warm water, not hot. The same idea applies to the scalp: comfortably warm. If the water is hot enough to turn your skin red, it is too hot.

Shampoo on the scalp, conditioner on the ends, warm water, blot don’t rub. Four habits you can keep every day at no extra cost.

Example: planning a week with a dandruff shampoo

Say your hair is straight, your scalp is oily, you wash daily, and your dandruff shampoo’s label says to leave it on the scalp for 5 minutes, twice a week (assumed numbers; use your own label).

Day	Shampoo	Time on scalp
Monday	Dandruff	5 minutes
Tuesday	Regular	Massage and rinse
Wednesday	Regular	Massage and rinse
Thursday	Dandruff	5 minutes
Friday - Sunday	Regular	Massage and rinse

Over a week the scalp gets 2 x 5 = 10 minutes of contact with the active ingredient. Use the 5 minutes to wash the rest of your body. What matters is waiting the full time on the label; rinse straight away and the active ingredient barely gets to work.

The AAD’s split by hair type: fine, straight or oily hair can be washed often, with the dandruff shampoo about twice a week. Coarse, curly or coily hair is washed as needed, with the dandruff shampoo about once a week and only on the scalp so the hair does not dry out.

Dandruff: what you can handle at home, and when to see a doctor

Over-the-counter dandruff shampoos use different active ingredients, such as zinc pyrithione, salicylic acid, selenium sulfide, ketoconazole, sulfur or coal tar. If one used to work and stops working, the AAD suggests alternating with a shampoo that has a different active ingredient. Two things to know: coal tar can discolour blonde, grey or white hair, and some medicated shampoos, especially coal tar ones, make the scalp more sensitive to sun, so wear a hat outdoors.

See a dermatologist when:

• dandruff does not improve after using a dandruff shampoo as directed
• it is severe, for example thick flakes or a lot of redness or itching
• the scalp is inflamed in patches, or hair is falling out in patches as well

Scalp flaking is not always plain dandruff. It can be seborrheic dermatitis, psoriasis, a fungal scalp infection or eczema, and only a doctor’s examination can tell them apart. This article is not a way to diagnose any of them.

If a dandruff shampoo used properly does not help, do not keep switching brands. Have a dermatologist check first.

Common mistakes

What people do	What happens
Scrub shampoo through the whole length	Dry, frizzy hair that tangles easily
Scratch the scalp hard with nails	Scrapes and irritation
Put conditioner on the roots (fine hair)	Flat hair that gets greasy fast
Rinse dandruff shampoo off straight away	Active ingredient not on the scalp long enough
Use very hot water	Dry, itchy scalp
Rub hair with a towel	Fragile wet hair breaks more easily

If you also wear gel nails or use products that can cause allergies, the way to watch for a reaction is similar: see Gel nail allergy: warning signs and how to lower the risk.

Sources

• Tips for healthy hair — American Academy of Dermatology
• How to treat dandruff — American Academy of Dermatology
• 10 hair care habits that can damage your hair — American Academy of Dermatology
• Dermatologists’ top tips for relieving dry skin — American Academy of Dermatology
• Hair cosmetics: an overview — International Journal of Trichology (PMC)