Hair Density: What It Is and How It Changes
Hair density means how many hairs grow in a given area of scalp, and it is only one part of how full hair looks. Strand thickness matters too, and both change with age. Research also shows that measured density depends on the scalp area, the person's background and the method used.
Here's what studies found.
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Key Takeaways
- In 1,414 women, density was highest at ages 20 to 30 and declined thereafter, while hair diameter rose until about 40 to 45 and then fell.
- Thinning became more noticeable from the mid 40s to the mid to late 50s, when a smaller diameter combined with falling density.
- In 23 volunteers, trichoscopy gave lower occipital density (163 per cm²) than biopsy (215 per cm²), so the two methods can't be used interchangeably.
- A systematic review on baseline density found variation across ethnicity, scalp region and measurement technique.
What Is Hair Density?
Hair density is the number of hairs per square centimetre of scalp. It is measured by photographs, trichoscopy (magnified imaging of the scalp) or biopsy.
Why Numbers Differ
There is no single "normal" density. It varies with scalp area, background and how it is measured, so comparing your number to a chart can mislead.
If You're Worried About Density
- Compare photos over time in the same light and angle.
- Ask a doctor to assess hair loss. They can use proper measurements.
- Consider thickness too. A drop in strand diameter changes how full hair looks.
What The Research Shows
Density, Diameter And Age
In 1,099 Caucasian women with self-perceived hair loss and 315 with no complaint, scalp hair diameter increased from ages 20 to 40 to 45 and then decreased, and density was highest at 20 to 30 and declined with increasing rate. Women who perceived hair loss had a faster fall in density. The authors proposed a combined "hair amount" metric and concluded that thinning becomes increasingly noticeable from the mid 40s to the mid to late 50s (Robbins et al., 2012).
Trichoscopy Against Biopsy
In 23 volunteers without alopecia, trichoscopy was performed on four scalp regions and a 4 mm biopsy was taken from the occipital area. In the occipital region, trichoscopy gave a density of 163.07 per cm², lower than the biopsy's 214.97 per cm², and a higher hair shaft diameter (74.52 µm against 68.65 µm). The authors concluded the methods cannot substitute entirely for each other, and the study set a reference for the adult Chinese population (Hu et al., 2022).
Baselines
A systematic review in the Journal of the American Academy of Dermatology is titled "Establishing baselines of hair density measurements: Variations across ethnicity, scalp region, and measurement techniques". PubMed doesn't include an abstract for it, so we can only report what its title says: that baseline density varies across those three factors (Buontempo et al., 2023).
Fine hair describes more than density alone; see what fine hair is.
See also: Turmeric for Hair and Scalp: What the Research Shows · Micro Bangs: What to Know Before You Cut
Frequently Asked Questions
What is a normal hair density?
There isn't one number. Density varies with age, scalp region, background and measurement method.
Does hair density decrease with age?
In the women studied, yes, after the 20 to 30 age group.
How is hair density measured?
By photographs, trichoscopy or biopsy. The two methods compared here gave different numbers.
References
- Robbins C, Mirmirani P, Messenger AG, et al. What women want - quantifying the perception of hair amount: an analysis of hair diameter and density changes with age in caucasian women. Br J Dermatol. 2012. PubMed
- Hu D, Tu P, Yang S. Comparison Between Trichoscopic and Histopathological Evaluations of Hair Parameters. Clin Cosmet Investig Dermatol. 2022. PubMed
- Buontempo MG, Sperling LC, Alhanshali L, et al. Establishing baselines of hair density measurements: Variations across ethnicity, scalp region, and measurement techniques: A systematic review. J Am Acad Dermatol. 2023. PubMed
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