In this article:
- Anatomy of hair
- The hair growth cycle
- Causes of hair loss
- What is a normal amount of hair loss for your age and gender?
Thinning hair is a common symptom of hypothyroidism. However, many other factors can contribute to your locks' thickness and health. For example, genetics, age, gender, skin conditions, and other health conditions can influence hair thickness. Because our hair is often a window into our overall health, it is essential to understand the driving force behind your thinning hair.
Overview of the anatomy of hair
Hair anatomy is so much more than what meets the eye. Essentially, there are two anatomical components to hair: the hair shaft and the hair follicle.
The hair shaft is what we see and feel. Keratin makes up each hair shaft, a hard protein surrounded by a protective cuticle (or outer layer). Certain habits like over-styling and chemical dying can break down the cuticle, causing hair to become brittle and break.
The hair follicle anchors your hair inside your scalp and contains the bulb and papilla. The bulb has cells that grow around the strand to increase length while the papilla directs blood supply to nourish the follicle for growth. We have thousands of hair follicles, and each follicle follows its hair growth cycle.
What is the hair growth cycle?
When it comes to learning about the reasons behind hair loss, an excellent place to start is with a general understanding of the hair growth cycle. Often, hair loss is due to something that disrupts the hair growth cycle. There are three phases of the hair growth cycle: Anagen, Catagen, and Telogen.
Also called the growing phase, anagen is roughly a 3-5 year period where hair strands lengthen. Our genetics largely determine the length of the growing phase. Most people can only grow their hair to a specific length before it stops growing.
This short transitional phase lasts only a few weeks. During this phase, the follicle stops nourishing the hair shaft. Once the follicle stops receiving blood, it ceases to grow and is called a club hair.
During the hair growth cycle's final phase, the hair enters a resting period of around three months. A new hair shaft begins to grow beneath the old follicle and eventually pushes the club hair out. Hair shedding completes the individual strand's telogen phase, and a new strand enters the anagen phase. Fortunately, each hair follicle follows its own growth cycle, so we don't lose all of our hair at once under healthy conditions.
Common causes of hair loss
Many factors can contribute to hair loss, and often it is a combination of several things.
Androgenic alopecia is the term for genetic-induced hair loss. Both men and women can suffer from this form of alopecia—the term used to describe any type of hair loss—and it is the leading cause of hair loss.
According to the American Hair Loss Association, androgenic alopecia accounts for over 95% of hair loss in men. Additionally, nearly 30 million women in the United States suffer from this form of hair loss. Androgenic alopecia may be due to an increased sensitivity to the dihydrotestosterone (DHT) hormone in the scalp, which shortens the hair growth cycle and shrinks hair follicles.
Experiencing some hair thinning with age is expected in both men and women. Most men will notice a significant change in their hair thickness by age 50. In contrast, women usually do not see a difference until after menopause. Some people with genetic hair loss may notice thinning as early as their teens or twenties.
We usually associate hair loss with men. However, at least 40% of women also struggle with hair loss. Still, women tend to have an easier time concealing these changes. While men are more likely to struggle with genetic causes of hair loss, women are more susceptible to hormonal changes that disrupt the hair growth cycle—for example, pregnancy, childbirth, breastfeeding, and menopause. Women are also more likely to have autoimmune conditions, where hair loss is a common symptom.
People who have undergone an incredibly stressful event—loss of a loved one, surgery, job change, childbirth, etc.—can develop telogen effluvium. In this condition, a good portion of hair suddenly shifts out of anagen and into telogen. Typically, three months after the stressful event, many people notice their hair starts to fall out. Fortunately, your hair will start growing again after the stressor has passed.
People with hypothyroidism commonly struggle with hair thinning. Thyroid hormones help signal hair follicles to grow. Interestingly, thyroid hormones are also responsible for the regeneration of our skin cells. Thus, people who do not have enough thyroid hormone have thinner, finer hair and skin.
Additionally, certain medications may affect your hair growth, including some antidepressants and birth control pills.
What is a normal amount of hair loss for your age and gender?
Mild hair thinning can be a typical sign of aging. Most men will notice hair thinning after age 50, and women commonly see changes after menopause—with an average age of 51. Typically, hair thinning occurs uniformly all over the head if it is related to aging. If hair loss is patchy or follows a pattern, it is not a sign of aging but may instead be related to a condition.
The American Academy of Dermatology states that it is normal to lose between 50-100 hairs a day. People under age 50 should heed the signs of hair loss early on and seek medical advice from their doctor or dermatologist to determine the cause of their hair loss.
Sometimes, hair thinning is reversible with the right medication or with lifestyle changes. For example, people with hypothyroidism may notice their hair begins to grow back after they have been on thyroid medication for some time. If you have hypothyroidism and find your hair thin and delicate, meet with your thyroid doctor to make sure you are on the right dose and type of thyroid medication.
A note from Paloma Health
It's not unusual to lose some hair each day, but if you're worried about excessive hair loss with hypothyroidism, meet with your thyroid doctor to consider lifestyle modifications and to determine if you're on the right dose and type of thyroid medication.