Your hair type is genetic. Here is what to do with that.

You and a friend have the same hair. Same curl, same length. She tells you what she uses, you buy it, and three weeks later your hair is limp and greasy while hers looks better than ever. The usual explanation is that you are doing something wrong. You are not.

“Hair type” describes what your hair looks like. What a product does to it depends on things you cannot see, and those are inherited. In twin studies, hair texture is up to 90 percent genetic, and the traits underneath it, how thick each strand is, how much oil your scalp makes, how well the strand holds moisture, come from the same place. Two heads of identical curls can be running on completely different settings.

What “hair type” leaves out

Curl matters because of oil. The oil your scalp produces has to travel down each strand to coat it, and on a curly strand it gets stuck at the bends, which is why curly hair runs dry at the ends. The curl aisle is built on that fact.

What the curl aisle cannot know is how much oil your scalp was making to begin with. Dermatologists say wash frequency depends on your scalp more than your hair, and the American Academy of Dermatology tells people to wash based on how oily they get, not on curl pattern. Your friend’s scalp makes very little oil, so the rich cream she swears by is exactly what her ends are missing. Yours makes plenty. The same cream lands on oil that was already there, and by lunchtime you look like you skipped a wash.

Strand thickness is a second dial. A thick strand takes protein treatments and a hot iron without complaint; a fine strand snaps under the same routine and collapses under products a thick strand barely notices. Density, meaning how many strands you have per inch of scalp, is a third, and it decides whether volume is a real problem for you or just a word on a bottle. None of these show up on a curl chart. All of them were set before you bought anything.

So the routine did not fail and neither did you. She was following her settings. You were following hers too.

What your DNA adds

Your genome holds those settings. Reading it tells you where you sit on each dial, which is enough to buy the right weight of product the first time instead of finding out over a year of half-used bottles. Curly hair on a low-oil scalp wants the heavy end of the aisle. Curly hair on a high-oil scalp wants the light end and more frequent washing than curl advice usually allows. Fine strands want little protein and low heat. Thick strands can take both. None of it is complicated. It has just never been written for you specifically.

Your genome also covers what no mirror can: where your hair is headed. Hair loss is about 80 percent heritable. It reaches roughly half of men by fifty, and plenty of women, for whom it usually shows as a widening parting rather than a receding line. The largest study to date found more than 600 regions of the genome involved. The advice to look at your mother’s father is partly right, because the single biggest gene sits on the X chromosome, which men inherit from their mothers. But most of the risk comes from both sides of the family at once, so a grandfather is a clue and not a forecast.

Greying works the same way. The first gene tied to it, IRF4, was found in 2016 and explains about a third of the timing. If you went grey early, it was mostly decided before the stress you blame, and no supplement was going to change it.

Thinning is the one worth knowing about early. The treatments that work are far better at keeping hair than growing it back, so the right time to start is before you would notice anything. The cue most people wait for, the shower drain or a photo from behind, arrives after that window. Missing it is not a disaster. It is a head start most people never knew they had.

What to do with it

Your routine. Match product weight to your oil and strand thickness, not your curl type or your friend’s shelf. Oily scalp, wash more and go lighter. Fine strands, keep protein and heat occasional. Thick and dry, the rich products are yours. The report will not pick your shampoo, but it will stop you buying the wrong category, which is where the money goes.

Your timeline. Hair loss is where the report earns its keep. It gives you a risk figure instead of a guess from your grandfather. If it is high, see a dermatologist in your twenties while there is plenty to keep, and bring the summary from your report. If it is low, walk past the scalp serums. Either way you decide on your own numbers.

Your habits. Genes set your sensitivities, not your outcome. Heat, bleach, tight styles and smoking cost more on some heads than others, and your report tells you which head you have. That is not a reason to give anything up. It is a reason to know what each habit costs you.

Your future self. Your genome does not change, but what we know about it does. New studies on hair loss, greying and texture get applied to your sequence as they land, without another swab. What your report says today is the least it will ever tell you.

This is information rather than a diagnosis. Hair loss that arrives suddenly, in patches, or with other symptoms has causes unrelated to the genes here, and is a reason to see a doctor.

The same reading, everywhere else

IRF4, the greying gene, is also part of how easily you freckle and burn. The study that found it turned up genes for eyebrow thickness and beard density along the way. Hair is the part of your genetics you can see from across a room. The rest, from how you respond to medications to how you sleep, is in the same file.

Lifecode reads all 6.4 billion letters of it once, then re-reads it as the science improves, so what it tells you about your hair at twenty-five is still being updated at fifty. That is why we built Lifecode.