Caps, haircuts, the full moon: true or false?

“Take that cap off, you’ll go bald.” “Cut it at the full moon and it’ll grow back stronger.” “A hundred brush strokes every night.” You’ve probably heard these from a parent, a hairdresser or a video. They sound like common sense. Yet most of them fall apart once you hold them up against what dermatologists say.

This isn’t just folklore. A dermatology team listed twelve common myths about hair loss, then searched the medical literature for evidence for or against each one. Their conclusion: for many of them, there’s very little evidence⁷. Here are the most stubborn ones, one by one. The ones aimed mostly at men, from hair gel to testosterone, have their own article: gel, sex, swimming pools, the male baldness myths.

Do caps make you go bald?

No. The French Society of Dermatology (SFD) puts it plainly: regularly wearing a helmet or a cap doesn’t make pattern hair loss worse¹. A team of Irish dermatologists who reviewed hair loss misinformation online lists wearing hats among the false causes: no evidence links it to hair loss².

The idea may come from a coincidence: when you start losing hair, you’re tempted to hide it under a cap. People see the two together and assume one causes the other.

A cap is actually useful. Where hair thins, the scalp gets sunburnt more easily. The SFD simply recommends a hat, a cap or any other headwear¹, and the Irish authors point out that hats protect people with hair loss from the sun².

Does cutting or shaving make hair grow back thicker?

It’s one of the most widespread myths, and it’s wrong. The SFD lists shaving your head with clippers to “strengthen” your hair among the practices with no proven effect on hair loss¹.

To see why, you need to know where a hair is made. It starts in the follicle, the small structure in the skin that produces it, grows for several years, rests, then falls out to make room for the next one³. Scissors and clippers cut the part above the skin. They don’t touch the follicle or its cycle, which decide how thick and dense your hair is.

So cut or shave for the look, for comfort, or because short hair suits you better. Just not in the hope of growing more hair back.

Cutting your hair at the full moon

The lunar calendar has its fans, among some hairdressers and in magazines. The SFD names cutting your hair at the full moon among the practices with no proven effect on hair loss¹.

If you like getting your hair cut on a particular date, nothing stops you. Just don’t expect any more from it than from a haircut on an ordinary Tuesday.

Headstands to get blood to the scalp

The idea sounds logical: upside down, blood rushes to your scalp, so the roots should be better fed. The SFD lists doing headstands to irrigate the scalp among the practices with no proven effect¹.

This tip keeps coming back on social media, alongside rosemary oil and onion juice. We’ve gone through viral hair loss tips one by one, with what the studies show for each.

100 brush strokes a night

It’s advice from our grandmothers: a hundred brush strokes every night for shiny, strong hair. The American Academy of Dermatology (AAD) is clear: hair never needs 100 brush strokes a day, that’s a myth⁴. It adds that brushing 100 strokes a day can cause split ends⁵.

Its advice: brush and comb only to style your hair⁴. And take care with wet hair, which breaks more easily when combed or brushed⁵. For other everyday habits, such as the hairdryer or straighteners, we’ve put together four gentler styling habits.

So brushing too much damages the hair shaft, but it isn’t what decides hair loss. The hairs left in your brush have mostly reached the end of their cycle: after their resting phase, they fall out anyway³. The Irish dermatologists also note that brushing and washing are blamed online without any evidence².

Shampooing every day

Lots of people space out their shampoos for fear of losing more hair. The SFD is clear: contrary to popular belief, shampoo doesn’t make hair loss worse¹. On a normal day, we lose between 50 and 100 hairs³. If you wash your hair every three days, you find the previous days’ hairs in the shower, which gives a misleading impression.

We’ve gone into all of this, with how often to wash depending on your scalp, in does washing your hair often make it fall out?

What really matters

If caps, the moon and the brush don’t decide anything, what does? Two things, mainly.

The first is heredity. The most common type of hair loss, androgenetic alopecia, comes from a particular sensitivity of the hair to certain hormones, and that sensitivity is largely inherited¹. We’ve explained how it’s passed down, from your mother’s and your father’s side.

The second is hairstyles that pull. If you often wear your hair tightly pulled back, the constant pulling can lead to permanent hair loss, called traction alopecia⁶. Braids, cornrows, ponytails and extensions worn all the time pull on the hair and can make it break. If the tension continues, the loss can become permanent⁵. And once a follicle is damaged, it can’t grow hair any more⁶.

The AAD therefore recommends wearing your hair loosely pulled back, or choosing a style that doesn’t pull⁴. The signs to look out for are covered in when your bun pulls too hard.

Finally, colouring, perms and relaxers damage the hair shaft. Over time, that damage can lead to hair loss⁶. You don’t have to give them all up: just space them out and avoid stacking them.

Judge by photos, not by advice

All these myths have one thing in common: people judge them by impression. You get a haircut and feel your hair is thicker. You stop wearing a cap and think you’re losing less. The mirror can’t settle it: the light, the angle and your hairstyle change from day to day.

If you want to know what’s really changing, take the same photo every week, in the same room, at the same distance, with dry hair. With Calvap, last week’s photo shows as a see-through overlay while you frame the shot, so your photos are comparable from one week to the next. You log changes to your habits in the journal, and you see on the timeline whether your part, hairline or crown changes in the weeks that follow.

It’s also the best way to sort what you’ve been told from what’s actually happening on your head.