What is hair made of? How much hair loss per day is considered abnormal?

Author: Zhang Jianzhong, Chief Physician, Peking University People's Hospital

The 13th Chairman of the Chinese Medical Association Dermatology and Venereology Branch

Reviewer: Wang Aiping, Chief Physician, Peking University First Hospital

Our skin is the outermost and largest organ of the human body, accounting for about 16% of body weight. In addition to the epidermis, dermis, subcutaneous fat and other structures, the skin also has some special appendage structures, such as hair, nails, sebaceous glands, sweat glands, etc. Today we will mainly talk about hair.

1. What kind of substance is hair?

No matter what your race is, whether you are white, black, or yellow, your body is covered with hair. These hairs include relatively small (about 0.5mm), non-pigmented, and not easily observed body hair, as well as relatively long and thick eyebrows, eyelashes, armpit hair, pubic hair, and head hair.

Eyelashes and eyebrows can grow to about 1 cm or even longer, and our hair can continue to grow and grow longer as long as you don't trim it. These hairs contain pigments. Generally speaking, white people's hair is often brown or golden, while Chinese and African people's hair is often black.

But no matter what color your hair is, no matter whether your hair is curly or straight, hair is essentially a kind of protein, a kind of keratin, which is a protein produced by keratinocytes. It can be divided into dozens of types, and our skin protein is one of them.

Figure 1 Original copyright image, no permission to reprint

Moreover, keratin is relatively tough. Sometimes when excavating ancient tombs, it is found that the muscles and organs of the ancient people’s bodies have disappeared, but the bones and hair are still there. In other words, our hair is actually very tough.

2. Why does our hair fall out?

We all know that if a tree wants to grow tall and not be afraid of being blown down by the wind, it must first take root in the ground. Only with solid soil and strong roots can the tree have the possibility of growing taller and more luxuriant.

By the same token, if we want our hair to grow on the scalp for a long time, first of all, the "roots" of the hair, that is, the hair follicles, must survive well in the skin on the top of the head.

The part of the hair buried in the skin and inside the hair follicle is called the hair root, and the part exposed outside the skin is called the hair shaft. Hair grows from the base to the end of falling off, all thanks to the nourishment of the hair follicle. There are also some sebaceous glands around the hair follicle that can produce a certain amount of oil to nourish the hair follicle and hair.

So how much hair can a person have? In fact, the number of hairs on each of us may be different. Some people have sparse hair, while others have dense hair. But on average, it is estimated that a person can have about 100,000 hairs.

These 100,000 hairs do not grow endlessly. Instead, their growth often has a certain periodicity, with a growth phase, a regression phase, and a resting phase.

Generally speaking, the growth phase of hair can last for 2-4 years, during which time the hair can continue to grow. After the growth phase, it will enter the regression phase, which lasts for 2-4 weeks. This period is when the hair stops growing and stops growing, which is equivalent to a "holiday" for the hair. Then, this batch of hair will enter the resting phase, which lasts about 3 months on average. At this time, the hair follicles will gradually move upwards, that is, the "roots" of the hair will become shallower and shallower, so it will fall off very easily.

Generally speaking, among all the 100,000 or so hairs we have, about 85%-90% of them are in the growth phase, about 10% are in the resting phase, and about 2%-3% are in the regression phase. So with such a large base of about 100,000 hairs, there will always be some hairs in the resting phase and fall out, so it is normal for us to lose 40-100 hairs every day. This is just the normal renewal of hair, the replacement of old and new, and we don't need to worry too much.

Figure 2 Original copyright image, no permission to reprint

Moreover, after the hair falls out during the resting phase, new hair follicles will be produced in the same area, and a new cycle will begin, maintaining growth for several more years.

Generally speaking, around the age of 20 is the peak period of hair growth. A person's hair volume, hair quality, density, curly or straight, dry or oily are basically determined around the age of 20.

3. What kind of hair loss should we be wary of?

As mentioned above, based on the proportion of hair in the resting phase, the normal amount of hair loss for a person should be around 40-100 strands per day.

Therefore, if we find that the number of hair loss exceeds 100, or even 200, 300 or more hairs fall out every day for several months, then there must be some abnormality.

In addition, there is another situation that deserves attention, that is, the hair quality. Hair loss is actually easier to observe for women. After a long period of time and a large amount of hair loss, women can clearly find that their hair has become thinner. However, men tend to have shorter hair, and some people are not easy to find it if they don’t observe carefully. Therefore, it is often the case that hair loss continues for a period of time before suddenly discovering that the hair has become thinner, thinner, and softer, and even the hair can no longer cover the scalp, and the scalp can be clearly seen. At this time, it is often suggested that this type of hair loss is pathological and needs to be taken seriously and go to the hospital for examination and treatment.