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Thickness should be a factor you consider when deciding everything from your haircut to the styling products you buy.

Shopping for shampoos, conditioners and styling products, you’ll often see products labelled for fine or thick hair. You’ve likely broached the topic of your hair’s thickness with your hair stylist. Hair professionals are exposed to clients with diverse hair, so they of course have a better gauge for strand thickness than the average person. Our own experience and research at hairID has taught us that professionals are often misled by their intuition, and most people don’t know the truth about the thickness of their hair.

We mentioned that thickness is important, and we’ll dig deeper into why that is in a later blog post, but first we want to impart some basic facts and definitions so you can better understand the terminology out there on this subject.

10 facts about hair thickness.

1. First off, we’ve noticed that there is frequently confusion surrounding the concepts of thickness and density, and we want to set the record straight. Density refers to the number of hair strands on your head. Thickness refers to the width of each individual hair strand.

2. Every person’s head has many hair strands, and they all vary slightly in thickness, ranging on average between 50-180 microns.

3. Thickness isn’t binary; your hair is not either thick or thin. There’s a spectrum, and your strands can fall somewhere in between.

4. Hair is not simply defined as thick or fine; it has a shape, too. Some have oval shaped hair strands while others have circular hair strands. DNA and ethnicity play a prominent role in hair shape and thickness.

5. Hair thickness is NOT ONLY a function of genetics, it’s also largely susceptible to environmental factors. Age, of course, is a major factor. For women, hair thickness peaks in their 40s and men in their 20s.

6. Thick hair is more likely to have a medulla. The hair is made up of cuticles, a cortex, and a medulla. The medulla is the innermost layer of the hair shaft, kind of like the marrow in bones. Everyone has cuticles and a cortex, but only people with thicker hair have medullas.

7. Science shows correlation between hair thickness and length. The hair growth cycle consists of four stages. The Angen Period, anywhere from 2-7 years, is the stage during which your hair grows. The length of this period ultimately determines how long your hair can grow; it also determines how thick your hair is. The longer the angen period, the thicker your hair.

8. Hair growth cycle is strongly linked to hormones. For women, significant hormonal fluctuation results in noticeable changes in hair thickness. For example, during pregnancy, women often benefit from thicker, fuller hair. After giving birth, though, they experience thinning hair or loss.

9. Thinner hair is harder to permanently wave. The structure of thin hair is harder to chemically alter than that of thick hair.

10. We see a lot of discussion out there, in magazine articles and in product marketing, of the impact a balanced diet has on hair. We can’t definitively claim that there is absolutely no correlation between a “healthy” lifestyle and the thickness, and thus the strength, of your hair, but if we’re being transparent, we must report that there is nothing in our research that indicates a solid link. We don’t want to tell you not to buy those vitamins that claim to do wonders for your hair, but in case you’re curious, we don’t buy them.