Alan Bauman, M.D., ABHRS, FISHRS
One of the most common questions I get asked in my hair restoration practice is “How Much Does Hair Grow in a Month?” The typical hair growth rate in humans is important to know because it can help predict when you are likely to see results from many hair growth treatments, both invasive (medications, laser, PRP, etc) and also hair transplantation.
Men or women who color their hair can easily judge their hair growth rates by looking at the length of their “roots” when it’s time for a color touch-up treatment. The “roots” reveal the amount of hair growth since the last color treatment. For example, the length of hair growth in six weeks which is grey or uncolored is usually quite obvious, and that length divided by the time between color treatments tells you how fast your hair has grown.
For example, if three weeks (i.e, 21 days) after a hair color appointment, that person noticed about ¼ inch (6.35mm) of roots showing, their growth rate would be approximately 0.3mm per day--which is the rate that most people consider average. In this particular case, after six weeks, the roots would measure about ½ inch.
If you ask people how fast their hair grows, some may respond that they feel their hair grows “super fast” and others may say their hair grows very slow. Some may report that their hair growth rates have slowed with age over time, and this concept is supported by the clinical literature. In fact, science also tells us that there are some variations between growth rates amongst different genetic groups or ethnicities. Interestingly, along with some other differences like hair curl for example, African hair is characterized by slower growth and lower density, Asian hair is characterized by low density and faster growth. Scientists found that African hair grew more slowly than Caucasian hair which grew more slowly than Asian hair. The difference between Asian and African hair growth rates equates to about 5cm or about 2 inches per year.
The study reported quite a high variation in rates:
Ethnicity: Rate Length/Day, Mean, +/- SD
African: 129-436 µm/day , 280, +/- 50
Caucasian: 165-506 µm/day, 367, +/- 56
Asian: 244-611 µm/day, 411, +/- 43
In 2016 Van Neste discovered that in Caucasians, thinner hairs grew slower than thicker hairs and that growth rates in women were higher than in men. Compared to hair of equal thickness in controls, subjects of both genders affected with patterned hair loss showed reduced growth rates. Men with patterned hair loss showed further reduction in growth rates as clinical severity worsened.
Initial testing and trials in the realm of MPHL (male pattern hair loss) did not investigate the effects of pharmaceutical interventions on hair growth cycling or hair growth rates. In 2019, Van Neste looked at male volunteers and what he discovered is that while finasteride and minoxidil had profound effects on hair growth cycling, slowing and reversing the progression of androgenetic alopecia aka male pattern baldness, he didn’t find any effect on hair growth rates.
At this time, we don’t have clinical data to answer the question of whether low-level laser therapy or PRP helps improve hair growth rates, but many patients report that these treatments increase hair growth rate, as evidenced by the fact they need color treatments more often.
Patients often wonder, "How long will it be until I see results from my treatment?" The answer is, that depends on how you’re looking at the scalp. For example, highly sensitive measurements such as HairCheck cross-sectional hair bundle trichometry is an excellent tool to judge the progress of a hair growth regimen. As early as six weeks, but more typically around 12 weeks, improvements from effective hair growth treatment can be measured. As hair density and hair caliber improve in the treatment zone, the hairs also continue to lengthen. HairCheck is an electronic caliper that gives an accurate measurement of the amount of hair and caliber of hair in the selected bundle. Hairs that were too short are not measured. However, as shorter hairs lengthen, more hair gets collected and measured in the bundle--which is a great indicator of response to treatment.
HairMetrix, the AI-powered microscope at Bauman Medical, can also provide a detailed evaluation of hair density and hair caliber since it counts and measures each individual hair in the zones being evaluated. This system provides a wealth of data for comparison between areas of the scalp initially for diagnosis purposes and also changes (results) between visits.
Improvements in both HairCheck and HairMetrix evaluations typically precede improvements in visual coverage and certainly hair volume, which require many more months of growth in order to judge results.
When it comes to hair transplantation, hair growth rates play an important role in judging the results from a procedure. Transplanted follicles remain dormant for months after the implanted FUE (Follicular Unit Extraction) grafts are healed. Once the transplanted follicles begin to produce hair--starting at around 4-5 months, the tiny stubble is felt at the level of the skin, but coverage still remains low. If the hair growth is 1cm per month from that point forward, it will take 6 months to see half of the result and a full 12 months to see 90 percent of the final result (or coverage) from a transplant procedure.