How to Determine Your Hair Type? Strand Shape, Thickness and Porosity

The answer to "how do I know my hair type?" isn't a single label, but four separate observations: strand shape, strand thickness, hair density and porosity. You can mostly work out the first three on clean, dry hair, by looking in the mirror and feeling it with your fingers. Porosity, however, can't be measured reliably at home; your hair's history of coloring, bleaching and straightening usually tells you more than the glass of water test. Whether your scalp gets oily is a separate question too, and it shapes your washing routine more than your hair type does.

How to determine hair type? Prepare your hair first

Styling products and blow-drying change both curl and volume. So make your observation after washing your hair with shampoo, without any leave-in products, and while your hair is air-drying naturally. Then answer the four questions below in order.

These four answers are independent of each other. You can have curly and fine hair, or straight and thick hair. That's why a one-word label like "normal hair" or "dry hair" often falls short when choosing care products.

Strand shape: straight, wavy, curly, tight coils

What determines the curl is the shape of the follicle the strand grows from. Curly strands come out of curved follicles and have more elliptical cross-sections, while straight strands have rounder cross-sections. For this reason, care products do not permanently change your curl pattern; chemical treatments do.

The best-known system numbers hair as 1 straight, 2 wavy, 3 curly and 4 tightly coiled, and uses the letters A, B, C to describe how tight the curl is. It's a practical language, but you need to know its limits:

• It relies on visual criteria, so two people can give the same hair different numbers.
• Many of these classifications were developed for marketing purposes in the industry and have not been independently verified.
• The same head can have several curl patterns. The temples, nape and crown may behave differently.
• It doesn't take density or porosity into account.

There are more objective methods that sort hair into eight groups by measuring curl diameter and the number of waves and bends, but these are tools for professionals, not for home use. What you need is not the number but this practical takeaway: as the curl tightens, the oil from your scalp has a harder time traveling along the strand, so curly hair feels drier than straight hair and suits washing less often. If you have several different curl patterns on your head, base your routine on the area that gives you the most trouble.

Strand thickness: fine strands and sparse hair are not the same thing

Thickness is the diameter of a single strand. Human hair diameter is generally given as roughly 50-100 micrometers. You can't measure this at home, but two rough methods give you an idea:

• Finger test: Roll a clean, dry strand between your thumb and index finger. If you barely feel it, it is likely fine; if you feel something distinct, it is likely thick.
• Thread comparison: Place a strand next to a sewing thread. If it is noticeably thinner than the thread, you are close to the fine side.

Neither of these is a measurement; both are estimates. Still, a person's own perception is not meaningless: in a study of 151 volunteers of European origin, those who described themselves as having fine hair had lower average strand diameter, hair density, strand stiffness and breaking load. For fine, straight hair, lighter products are therefore recommended; excess product easily makes hair look greasy.

Curl and thickness don't always go together. In European volunteers, curlier hair was found to be thicker, while in strands of African origin the diameter is reported to decrease as the curl increases. Don't choose products based on the assumption that "curly means thick."

Density: number of strands on your head

Density measures the number of hair strands on the scalp, not the strands themselves. One review gives the number of follicles on the head as roughly 90.000 to 120.000, depending on origin. Since you can't count them one by one, observation is enough:

• Part your hair down the middle and look in the mirror. If your scalp shows as a wide line at first glance, your hair is on the sparse side; if it's hard to make out, you're on the dense side.
• The thickness of a ponytail is also a rough clue, but it is affected by hair length and curl.

Density directly determines how much product you need. Dense, thick hair needs more care product, and you may need to apply it in sections. On fine hair, excess product shows quickly, so it's easier to start with a small amount.

There's an important distinction here: naturally sparse hair is a hair characteristic, whereas thinning that develops over time is not. If your hairline is widening over time or your hairline is receding, this isn't a hair type question but something to take to a dermatologist.

Porosity test: how reliable is the glass of water?

Porosity is the amount of space within the strand where water and chemicals can enter. It is low in hair that has never been chemically treated; bleaching, coloring and chemical straightening increase this value. In one laboratory measurement, the surface area of the hair nearly tripled within the first minute of bleaching. In another study, average porosity was about 3 percent in untreated hair, and about 12 percent after bleaching followed by acid straightening. So high porosity is often not an inherited type, but a measure of damage.

A common method online is to place a strand in a glass of water: if it sinks, it is considered high porosity; if it floats, low porosity. This test is very open to misleading results:

• A hair strand is already denser than water. What keeps it floating on the water's surface is surface tension, not the condition of its pores.
• Oil and product residue on the strand change the result. A well-maintained or oily strand may float even if it is porous.
• A strand with damaged surface gets wet faster and may sink, but this measures surface, not pore size.
• The time you leave it in the glass can also change the result.

In laboratories, porosity is measured by gas absorption, dye absorption, or the rate at which the strand dissolves in a specific solution. There is hardly any solid study showing that the glass of water test matches these measurements. So you can treat it as a bit of fun, but don't base your product decisions on it.

The questions that are more useful at home are these:

• Has your hair been bleached recently, or has it had permanent color or chemical straightening? If so, assume the treated part is highly porous.
• Are the ends different from the roots? On the same strand, the ends and the roots are not the same. Hair grows about 1 cm a month, so the end of a 30 cm strand has been exposed to sun, friction and processing for more than two years.
• Does your color fade faster than expected and look darker? The more the cuticle scales are lifted, the easier color goes in. This is a clue, not proof.

Scalp is a separate question: oily or dry?

Hair type relates to the strand, while oiliness relates to the scalp. Very dry-ended hair can have oily roots at the same time. As a rough measure, count how many days after washing your roots get oily enough to bother you. If they get oily within a day, your scalp is on the oily side; if they stay comfortable for a few days, it's medium; if they last about a week, your scalp produces little oil.

Flaking alone does not mean "dry scalp." Not washing your hair often enough, or using creams and oils that don't suit your hair type, can also contribute to flaking. If flaking persists, it's wiser to see a dermatologist before changing cosmetic products.

Turning the result into care

Observation only helps if it turns into a decision. The table below is a starting point compiled from general recommendations; adjust it to how oily your scalp is. For the order of steps, see our hair care routine article, and for product types, visit the hair care page.

No matter your hair type, excessive heat can cause damage. If you use heated tools, check the settings and frequency in our heat protectant guide. Hair type makes no exception here.

Does hair type change over time?

Yes, it can change, so don't blindly stick to the answer you had a few years ago.

• Age: As we age, sebaceous glands become less active. After menopause, androgen levels drop, so oil production decreases too, and washing less often may become suitable.
• Chemical treatments: Bleaching, coloring and straightening increase porosity and can also change the curl. Until the treated part is cut off, two different structures coexist in your hair.
• Length: As hair grows longer, the ends age. Hair that's fine in a short cut can feel dry at the ends when it's long.

If your hair has become noticeably thinner in a short time, is falling out in clumps, or you have a bald patch, don't treat it as a hair type change. For large losses occurring within a day or two, see a dermatologist immediately; for thinning that progresses more slowly, don't wait too long to see one either.