Male pattern baldness is the number one cause of alopecia, or hair loss, in men. As suggested by its more technical name, androgenetic alopecia, the condition results from certain hormones, which are collectively known as androgens, and genes that influence how hair responds to androgens.

The primary cause of hair loss in women is also a form of pattern baldness, called female pattern hair loss. Most men and women are genetically predisposed to developing pattern hair loss because they inherit genes for the trait. This form of hair loss typically occurs between the ages of 20 and 45 in the majority of patients, but can occur at a very young age and may continue throughout one’s life.

Male pattern baldness generally starts with a receding hairline and a thinning crown, and can range from partial loss to a horseshoe-shaped area of hair remaining only at the sides and back of the head. This animation will help you better understand why and how hair loss occurs as a result of male pattern baldness.

A typical hair consists of the shaft, which is the part you can see, and the root, which resides in a hair follicle. The hair shaft is non-living tissue, and only matrix cells in a region at the root, surrounding what is known as the dermal papilla, grow and divide, gradually pushing the elongating hair outward.

The numbers of hairs on a person’s head varies by hair type and race, but a typical range is 100,000 – 150,000 hairs on the scalp. Each day, an average of 50-100 hairs fall out of hair follicles as part of the normal growth process.

Hair that is lost is continually replaced by new hair, which grows in a cycle. When the hair growth cycle is disrupted, and more hairs are lost than regenerate, thinning hair and possible baldness result.

The hair growth cycle includes three phases, known as the anagen, catagen, and telogen phase.

The anagen phase is the longest, lasting between two and eight years. During anagen phase, the hair grows actively from matrix cells in the bulb, where the dermal papilla is nourished by blood vessels.

The next phase of the growth cycle is the catagen phase. This is a short, two to four week transitional period in which the hair stops growing, and the lower portion of the hair follicle retracts up to the level of the arrector pili muscle. The dermal papilla is pulled until it breaks away and regresses, detaching the upper portion of the follicle from the blood supply. At this point, the hair stops growing.

The last phase of the growth cycle, the telogen or resting phase, lasts two to four months while the dermal papilla is in a resting state. Following the telogen phase, the hair follicle reattaches to the dermal papilla and the follicle re-enters the anagen phase. As a new hair begins to grow, the old hair is pushed out of the follicle.

Normally, about 10-15% of follicles are in the telogen phase. With the onset of male pattern hair loss, this number can increase to 20% or more.

The shift occurs when a type of androgen hormone, dihydrotestosterone, or DHT, binds to hormone receptors on the dermal papillae of hair follicles. When DHT contacts a hormone receptor in the dermal papilla, it activates pattern hair loss by disrupting the normal growth cycle.

The affected follicle spends more time in the resting (telogen) phase, has a shorter growth (anagen) phase, and it physically shrinks in size and diameter and fails to grow. The follicle is still alive and connected to the blood supply, but its hair producing ability is diminished.

As a consequence, hair production slows, weaker and shorter hair is produced, and some follicles shut down completely. The shorter growth cycle causes more hairs to be shed than are produced, which causes balding to begin and become more obvious.

If hair loss is influenced by natural hormones, you may be wondering why some people are more inclined toward male pattern baldness than others. Both men and women produce androgens, and the hormone testosterone is actually a precursor to the female sex hormones estrogen and progesterone.

Testosterone is converted to DHT by an enzyme known as alpha-5 reductase, in the hair follicles, adrenal glands, and the male prostate and testes. In addition to the prostate and testes’ role in increasing DHT levels, men also have a greater number of androgen receptors in their dermal papillae than women.

These factors combine to make this form of hair loss more common and more severe among men. The reason the amount of hair loss is not equal among men is because those with the genetic predisposition for male pattern baldness have a greater number of androgen receptors for DHT to contact.

Genetic material within each cell is stored in chromosomes. Among the 23 pairs, males have one X and one Y sex chromosome, whereas females have two X chromosomes. The androgen receptor gene resides on X chromosomes, but the genetic component of male pattern baldness is not as simple as once believed.

People once thought that if your grandfather on your mother’s side was balding, you had a 50% chance of inheriting the trait – and here’s why. Your grandfather is male, so he has one X and one Y chromosome. Your mother is female, so she inherited two X chromosomes: one from your grandfather and one from your grandmother. You inherited one of her X chromosomes, so you have a 50% chance that you received the X chromosome with the balding trait that came from your grandfather.

However, more recent evidence suggests that a variety of genetic and environmental factors may be involved. A person whose father is bald is also very likely to lose their hair, and the genetic component for this is not completely understood.

For those who are genetically predetermined to exhibit male pattern hair loss, there is usually a progression from a receding hairline to a particular degree of balding. This process depends on where hair follicles are more susceptible to balding on an individual’s scalp.

A tool known as the Hamilton–Norwood scale helps classify the different ways male pattern baldness occurs, and it gives a relative measure of the degree of hair loss. Hair loss is divided into seven different categories. A full head of hair with little to no hair loss is signified as Type I. Complete loss of hair along the front and crown, where only a small ring remains around the sides and back of the head is signified as Type 7. Select any example to see the hair loss progression for that particular type.

Some men prefer to conceal, stop, or even reverse hair loss due to male pattern baldness. Fortunately, effective options for disguising or restoring lost hair exist today. These treatments fall into three broad categories: surgical treatments, prescription medications, and cosmetic treatments.

Beware that a variety of over-the-counter and herbal remedies claim to slow hair loss or grow back hair. Evaluate the claims carefully, and keep in mind that while there are effective approved treatments, there are also many ineffective treatments being marketed today. Consulting a hair restoration professional to find a treatment option for your particular lifestyle and hair loss pattern is the best method for obtaining the results you desire.