Static hair in autumn: what causes it and what changes it

In short: if your hair starts flying as soon as the heating is turned back on, it is neither your shampoo nor a sudden fragility. It is physics - friction, and air that has become too dry to dissipate charges. Here is what is really happening, along with a few simple steps (including a change of material) that make all the difference.

Every year, it is the same sequence. At the end of September, the radiators come back on, the sweaters come out again - and in the morning, a strand sticks out to the side, the brush crackles, and the lengths cling to the coat collar. We blame the product of the moment and buy yet another hair mask. I will be frank: the problem is almost never there.

What really happens when a hair becomes “electrified”

When two materials rub against each other, they exchange electrons. This is the triboelectric effect: one ends up with an excess of negative charge, the other with a deficit. Your hair rubs against a pillow all night, and against a collar, sweater, scarf, or brush all day. It becomes charged continuously - in summer and winter alike.

The difference lies in what happens next. In slightly humid air, each hair fiber carries a microscopic film of water that conducts electricity: the charge flows away, disperses, and disappears. In dry air, this film becomes thinner. The charge remains. And because all your strands carry the same charge, they repel one another - that halo of hair standing on end is nothing more than that.

That is why the phenomenon is seasonal rather than capillary: it is not the hair that has changed, but the air around it.

Why autumn is the worst time of year

Cold air contains little water vapor. When it enters a room and is warmed by ten or fifteen degrees, its relative humidity plummets. A heated interior commonly goes from 50-55% relative humidity in September to 30%, sometimes less, within the first few weeks of heating. Yet it is precisely below this threshold that charges stop dissipating: above 60% humidity, static electricity is a non-issue; below 30%, it becomes a daily occurrence.

Three aggravating factors occur at the same time, and it is this combination that makes October so unpleasant:

• Heating, which dries out indoor air - and, along the way, the fiber itself. I discussed it with Colette in her article on dry air and bed linen.
• Sweaters and scarves, often made of wool or acrylic, are two champions of charge transfer, rubbing against the lengths at shoulder height all day long.
• Hair already weakened by summer - sun, salt, chlorine - so more porous and rougher, with cuticles that are less tightly closed: more friction, more charge.

The factor we forget: the material touching your hair

A lot is said about hair care. Very little about surfaces. Yet over twenty-four hours, your hair spends six to eight hours in constant contact with a single material: your pillowcase.

Not all fibers behave the same way when it comes to static electricity, and the decisive criterion has a technical name: moisture regain - the amount of water a fiber naturally retains in a standardized atmosphere. The higher it is, the more slightly conductive the fiber remains, and the more charges dissipate instead of accumulating.

This last point is worth pausing over, because it explains a very common disappointment. “Satin” is not a material; it is a weave - one that produces a shiny, slippery surface. Satin can be woven from silk... or polyester. Visually, it's easy to confuse them. Electrically, the difference is clear: a polyester satin pillowcase glides well but retains virtually no moisture, so it accumulates charges instead of letting them dissipate. Many people buy a “silky” pillowcase to combat static hair and get the opposite result. That's also why we never talk about silk without discussing momme: the weight and the actual fiber are all that matter.

A word of honesty, because this Journal isn't here to sell you empty promises: to my knowledge, no clinical study has specifically measured the effect of a silk pillowcase on static electricity in hair. What I describe here concerns textile physics - moisture regain, coefficient of friction, and the triboelectric series - which is well documented. The mechanism is sound; don't let anyone promise you a figure.

My routine for dry nights

You gain the most at night, because it is the only time when contact lasts for hours without interruption.

1. Change the surface before changing the products. A mulberry silk pillowcase between 19 and 22 momme checks both boxes at once: little friction and proper moisture retention. It is the step with the best effort-to-results ratio.
2. Never go to bed with soaking-wet hair, but do not over-dry it either. Finish drying with warm air, not hot air: dried-out hair builds up more charge.
3. Tie it loosely. A loose braid or low bun secured with a silk scrunchie limits the strands rubbing against the pillow - and avoids the mark left by a tight elastic.
4. For curly, coily, or very dry hair, add a silk sleep bonnet: it completely insulates the lengths from the duvet cover and sleepwear.
5. A drop of vegetable oil on the ends in the evening. The lipid film slightly weighs down the fiber and reduces its tendency to fly away when you wake up.
6. Monitor the humidity in the room. A small hygrometer costs a few euros; aim for 40 to 50%. A bowl of water on the radiator, a plant, or laundry drying in the room is often enough to raise it by ten points.
7. Put away the plastic brush in favor of a wooden or horn comb, especially in the morning on dry hair.

And during the day, three habits

• Blame the sweater, not the shampoo. Acrylic and wool rub against the lengths all day. A silk scarf tucked under the collar acts as a buffer - that is, incidentally, one of the reasons it has always been worn.
• Line your winter hats. A wool hat worn directly against your hair is a charge-generating machine; a silk lining radically changes how your hair behaves when you get back inside.
• Forget the anti-static spray. Simply run slightly damp palms over the lengths, or mist them with a cloud of water from a distance: you restore the conductive film in three seconds.

What silk will not do

It does not nourish the hair: it deposits nothing; it simply avoids being harsh on it. It does not replace humidifying an overly dry room. And it has nothing to do with seasonal autumn hair loss, which follows an entirely different mechanism - if your hair has been falling out for more than three months or is visibly thinning, you should see a healthcare professional, not use a pillowcase.

What it does, however, it does every night, effortlessly, for years. That is exactly the kind of habit I like: invisible and cumulative.

Frequently asked questions

Does a polyester satin pillowcase work just as well?

For friction, it offers a real improvement over cotton. For static electricity, no: polyester retains virtually no moisture (around 0.4% compared with 11% for silk), so charges build up instead of dissipating. That is precisely what we are trying to avoid in autumn.

Which momme weight should you choose for a pillowcase?

19 momme is the right balance between flexibility and durability; 22 momme offers a denser feel and better long-term shape retention. Below 16 momme, the fabric is too lightweight to withstand frequent washing.

Do you also need a silk duvet cover?

Especially useful if you sleep on your side or if your lengths regularly slip under the duvet. Otherwise, start with the pillowcase: that is where contact is longest and most consistent.

How often should a silk pillowcase be washed?

Every week, just like a regular pillowcase. Cold wash, gentle detergent without enzymes, protective mesh bag, dry flat in the shade. Fabric softener is not necessary - and it would weigh down the fibers.

How long before seeing a difference?

As for static electricity, from the very first dry night: it is an immediate physical effect, not a treatment. For the overall appearance of the lengths - frizz and ends - allow three to four weeks instead.

Getting started

If you change just one thing before the first real weeks of heating, change the surface your hair rests on overnight. Our mulberry silk pillowcases are available in 19 and 22 momme, in French and international sizes. The rest - hygrometer, wooden comb, scarf under the collar - will follow naturally.

— Mei, for the StudioSoie Journal