As the temperatures drop, more and more of us are reaching for hats to keep us warm. For those who have experienced hair loss, hats become an even more vital part of the winter wardrobe. Or has wearing hats too often actually been the cause of their thinning hair? The verdict is still out on that hypothesis, but to understand the mechanisms and causes of hair loss, let’s take a look at its microanatomy.
What is alopecia?
Hair loss is a common concern. Alopecia – the loss or lack of hair where hair normally grows, which includes both medical conditions and common balding – is a huge and growing concern for many individuals. This is evidenced by the $4.6 billion product market size for hair loss treatments projected by the year 2030. Although hair loss itself does not present a threat to health, the negative psychological impact of alopecia is often significant, affecting self-esteem and causing stress and anxiety. While some forms of alopecia are permanent, others are not and can respond to medical intervention.
What is the anatomy of hair?
To understand hair loss, we must first take a look at the anatomy and physiology of hair growth, beginning with the skin. It is comprised of two layers:
- Epidermis – The outermost layer of the skin. It forms a waterproof barrier between the body and the external environment, which resists friction and microbial invasion and prevents water loss.
- Dermis – The much thicker layer immediately beneath the epidermis. It is responsible for the elasticity and strength of skin, supplies the epidermis with nutrients, and plays an important role in thermoregulation.
These two layers rest on the hypodermis, also known as the subcutaneous layer, which is composed of connective tissue that contains fat, blood vessels, and sensory receptors. It functions as a protective cushion and insulator.
Hair grows from the depths of the dermis but has its origins in the epidermis. Hair is part of the skin’s accessory structures and performs various vital functions, including protecting the body, aiding in thermoregulation, and assisting in the relay of sensory information to the brain.
Hair is made up of dead, keratinized epithelial cells connected by proteins. Dissecting the hair reveals its complex internal structure with three layers of cells: the medulla, cortex, and cuticle. These cells are arranged in concentric rings.
The structure of hair can be divided into three anatomical regions:
- Shaft – The region of hair extending beyond the epidermis.
- Root – The region of hair which penetrates into the dermis, deep to the shaft.
- Bulb – An onion-shaped structure deep in the dermis, containing several structures that aren’t found in other parts of the hair. This is the site for hair growth.
The root and bulb are surrounded by additional layers called the hair follicle. The hair follicle is innervated by a plexus of nerves that relay sensory information from the hair to the brain.
Also associated with each hair follicle is an arrector pili muscle. It is responsible for the hair on your body standing on end when you’re cold, frightened, or your emotions are otherwise running high. These smooth muscle cells extending from the hair follicle to the papillary layer of the dermis, and innervated by the nervous system, are responsible for what are commonly known as “goosebumps.”
What are the hair growth cycles?
Hair grows in continuous cycles, and each cycle can be divided into three phases:
- The anagen phase is the growth phase, lasting 2-7 years. It’s when cells in the hair matrix multiply and divide rapidly, pushing up existing cells which then keratinize and die, forming hair. At any given time, about 85 to 90% of hair on the head is in this growth stage.
- During the catagen phase (2-3 weeks), the cells in the hair matrix stop dividing, the hair shaft loses its connection to the papillae, and the follicle shrinks.
- In the telogen, or resting phase, metabolic functions are reduced and the hair falls out after about three months.
What factors can impact hair growth?
Hair growth can be influenced by multiple factors. Different hormones affect the hair growth cycle in different ways, leading to either excessive growth or loss of hair. Genetic factors, such as inherited predisposition or mutation in cell-signaling pathways can impact the regulation and regeneration of hair follicles. Lifestyle and nutrition also play critical role in hair growth, as malnutrition or unhealthy lifestyle can trigger hair loss. In addition, as people age, the growth rate and density of hair decreases.
What are the different types of hair loss?
Hair loss can be either permanent (known as scarring, or cicatricial alopecia) or reversible (known as non-scarring, or non-cicatricial alopecia).
Scarring alopecia is the rarer of the two types, necessitating the care of a dermatologist. It is often caused by autoimmune diseases or trauma that damages the hair follicle.
Nonscarring alopecia is more common and can typically be treated by a physician. Androgenetic alopecia is the most common type and is commonly known as male or female pattern baldness. Biological males with this type of alopecia typically experience hair loss around the hairline and at the top of the head, while biological females usually endure an overall thinning of hair with the hairline mostly left intact. Androgenetic alopecia affects 80% of males and 50% of females under the age of 70. It’s often caused from a genetic sensitivity to androgens (steroid hormones such as testosterone), but other genetic and aging factors can also be influential.
Regardless of individuals’ different circumstances, hair loss can be a distressing condition for many, contributing to serious psychological impacts like anxiety, depression, or a loss of confidence or sense of identity.
What are treatment and management options for hair loss?
Luckily, there are a few options available to help with hair loss. Topical corticosteroid treatments, such as minoxidil, are the most commonly used interventions as the first line of defense against hair loss. Minoxidil is FDA-approved to fight androgenetic alopecia, but is often used off-label to treat other forms of alopecia as well. It works by increasing blood flow to the area of application, which stimulates growth factors, such as vascular endothelial growth factor (VEGF), for supporting hair regeneration and prolonging the anagen, or growth phase.
In recent years, there has been a growing focus on developing hair-loss treatments that leverage advanced medical therapies. An example is mesenchymal stem cell therapy, which uses stem cells from fat or bone marrow to stimulate the hair follicle and repair damaged scalp tissue. Gene therapy, in which nucleic acids are used to alter gene expression, is also being explored. And scientists have had success using advanced tissue engineering to regenerate hair-producing skin and generate new, functional hair follicles. While these advanced therapies have shown promise in preclinical trials, more research is needed to verify their efficacy for use in alopecia treatments.