Let's start from the beginning, hair grows out from a structure called “hair follicle” which looks like little pockets in our skin and extends from the epidermis down into the dermis. Hair follicles formed around week 10 of our gestacional development (in utero, thanks Mom!). At the moment of birth, we have about 5 million hair follicles (100-150K on our scalp). We are born with the maximum amount of hair follicles that we will ever have as no new hair follicles are formed after birth.
Science Spiel™: Hair density depends on both the number of hairs per area of skin and hair thickness (diameter of an individual hair). Hair diameters are determined by our genetic background. Thus, the thickness of European hair ranges between 57-90 micrometers while Asian hair can be as thick as 120 micrometers. Everyday we lose an average 75 hairs. This is normal and due to the fascinating hair follicle physiology. Let me explain, hair follicles continuously grow hair for 2-8 years (0.4 mm per day). The length of this growth (anagen) phase explains why some people can grow longer hair than others. In my case my hair had never reached pass my shoulders, suggesting that my hair follicles are not working continuously for 8 years (lazy ones!). At some point and due to unknown reasons, hair follicles take a reversible break (go dormant for 4-6 months) resulting in hair-producing cells destruction and the fall out of the existent hair. This growth/dormant cycle is not synchronized among adjacent hair follicles triggering a mosaic pattern in the scalp. This is the reason why we may notice hair thinning (or hair loss) in unique scalp areas at a certain point in time. In a healthy young adult, 80-90% of the hair follicles are in the growth phase.
Beauty Spiel™: the amount of hair and the thickness of individual hairs are equally important to get a healthy hair look. It is totally normal to lose between 50-100 hairs per day. We must take care of our hair follicles (hair producing units) as we cannot replace the ones we have lost!
I will focus on female hair loss, which has its onset during the reproductive years and continues progressing slowly with age.
Science Spiel™: The mechanisms behind female hair loss are not completely understood, though genetic, hormonal and environmental factors are likely to be involved. One of the early alterations in hair loss is the shortening of the growth phase due to a combination of limited blood supply (lower number of capillaries) and an imbalanced growth factors/cytokines ratio. These alterations also promote apoptosis (non-inflammatory cell death) resulting in a net decrease in hair follicle density (AKA hair loss). Indeed, by the age of 25 our hair follicle density had experienced a 45% decrease (from 1,100 follicles/cm2 as a child to 600 follicles/cm2). Hair follicle density continues shrinking reaching 300 follicles/cm2 between the ages of 30 and 50. In addition to lower number of hair follicles (less hair), our hair becomes thinner and unpigmented (white hairs) due to a combination of the shorter growth phase and a miniaturization of the dermal papilla (the size of the papilla determines the thickness of the hair).
Beauty Spiel™: hair loss is a combination of less amount of hair and fine (white) hair. If left untreated, hair loss will be irreversible.
Science Spiel™: 1. Hormonal Factors: Contrary to what people may think, the role of dihydrotestosterone (DHT) in female hair loss is not very clear. DHT inhibition effectively treated hair loss in male but did not move the needle for their female counterpart. Promising new insides suggest that aromatase, an enzyme with anti-androgenic action, may play a significant role at preventing female hair loss. Aromatases convert androgen into estrogens … and we all know how good estrogens are for our hair! 2. Environmental Factors: inflammation in the upper part of the hair follicle strongly suggest the role of external factors such as solar radiation, pollutants and changes in the microbiome in hair loss. In addition to these factors, we should add artificial dyes, hair sprays and the daily heat from hair dryers, irons and curlers …
Beauty Spiel™: female hair loss has a hormonal component that is different from male hair loss (as we all should assume). Therefore, we need products design for us. Hair loss is not a one size fits all! The more that I learn about hair loss the more that I think we need to have a daily hair care routine similar to what we do for our faces.
Fun Facts about hair: 1. Genetic research suggested that humans become “hairless” around 1.7 million years ago. 2. There are 3 basic types of human hair: terminal hair (thick and pigmented) which grows on the scalp, eyebrows and eyelashes; vellus hair (thin, short, unpigmented) which grows everywhere else and intermediate hair which is a mixture of the other two that can be found on adult arms and legs. 3. Leg hairs (which are short and fine) only grow for about 2 months and armpit hairs make it to 6 months.