Health Science | Why do you lose your hair at a young age? (Part 1)

I never thought that my hair would run away from home at such a young age. My hair was so voluminous back then, but now it is bald like a Christmas tree. In fact, the current baldness is not sudden. Let Dr. Liu from the Dermatology Department take you to learn about hair .

01 Types of Hair

There are two types of human hair: terminal hair and vellus hair. Terminal hair: coarse and hard, dark in color, containing medulla, divided into long hair and short hair. Long hair includes head hair and armpit hair, while short hair includes eyebrows and nose hair. Vellus hair: fine and soft, light in color, without medulla, mostly found on the trunk. The thickness, length, density and color of hair vary with the body part, age, gender, physiological state, race, etc. A normal person has 60,000 to 100,000 hairs.

02 Hair Growth Cycle

Hair grows about 1 cm per month; a normal person can shed about 70 to 100 hairs per day. Hair growth is cyclical and is divided into the growth phase, regression phase, and resting phase.

1. Growth period: 70%-90% belong to the growth period. The average growth time ranges from 2 to 6 years. It is characterized by continuous growth and then enters the regression period.

2. Catagen: Less than 2% of the hair is in the catagen phase. The hair follicles no longer undergo cell division and produce hair. The cells gradually die and gradually move to the surface of the scalp. The catagen phase of hair generally lasts about 2-4 weeks. At this time, the hair stops growing, falls off easily, and then enters the resting phase.

3. Telogen: About 15% of hair is in the telogen phase, and the hair has completely stopped growing until it falls out. Generally, the telogen phase of hair lasts for about 2-3 months until a new hair follicle cycle begins. As we age, the number of hair in the growth phase gradually decreases, while the number of hair in the regression and telogen phases gradually increases, especially in men.

03 The relationship between hair follicles and sex hormones

The effect of androgen on the facial, beard, chest and limb hair is opposite to that on the head hair. The continuous effect on the vellus hair will make the hair thicker, longer and darker, becoming colored hair. The continuous effect of androgen on the hair will make it shorter, becoming colorless vellus hair.

04Classification of hair loss

Scarring alopecia: a type of disease that causes permanent and inflammatory destruction of the hair follicles and sebaceous glands, with unknown etiology. It is divided into four types: lymphocytic, neutrophilic, mixed, and nonspecific. Its characteristic change is the disappearance of the hair follicle opening. Histopathology shows that the hair follicles and sebaceous glands are damaged and gradually replaced by fibrous tissue, and the hair cannot grow again after falling off.

Scarring alopecia can be divided into primary and secondary types.

① Primary: A type of disease that causes permanent and inflammatory destruction, the hallmark change of which is the disappearance of the hair follicle opening.

② Secondary: Hair loss secondary to drug, chemical, radiation damage or local scalp diseases.

Non-scarring hair loss: including common androgenic alopecia and alopecia areata, etc. Classification based on expected results: According to the damage to hair follicles, it can be divided into permanent hair loss and temporary hair loss.

Permanent hair loss : genetic factors; deficiency or imbalance of male hormones, scarring alopecia, etc.

Temporary hair loss: malnutrition, certain inflammatory skin diseases, endocrine disorders, etc.

05 Causes of hair loss

Androgenic alopecia : commonly known as hereditary alopecia and seborrheic alopecia. Currently, 95% of people with hair loss suffer from androgenic alopecia. This type of hair loss is closely related to genetic factors. The hair loss sites are generally concentrated on the top of the head and forehead, and are often accompanied by greasy scalp. Androgenic alopecia is a chronic hair loss. Hair loss starts from the top of the head and forehead, and the area gradually expands, the degree of thinning becomes heavier, and the hair loss increases. Generally, it can develop into severe hair loss in 1-5 years. The medical community has proved that the hair follicles of people with androgenic alopecia are more susceptible to the influence of DHT (dihydrotestosterone) and shrink. Reducing the concentration of DHT is a feasible solution to improve androgenic alopecia.

Neuropsychiatric hair loss : excessive mental stress often leads to increased hair loss. Mental stress may cause blood microcirculation disorders in the scalp, resulting in poor blood circulation in the hair papilla and premature entry into the resting phase. Organic diseases of the central and peripheral nervous systems also often cause hair loss.

Endocrine hair loss : Hair growth is affected by a variety of hormones, so endocrine disorders can cause hair loss and aggravate androgenic alopecia. Postpartum hair loss in women is endocrine hair loss.

Nutritional alopecia : Hair is an outward manifestation of physical condition. Malnutrition and metabolic abnormalities can cause changes in hair quality and color. Severe malnutrition can even lead to diffuse hair loss.

Pathological hair loss : Some diseases may cause hair loss, such as hyperthyroidism, anemia, chemotherapy, autoimmune diseases, etc.

Physical hair loss : including mechanical stimulation and exposure to radioactive substances. Long-term strong combing, using too tight hairpins, excessive braiding, etc. can cause traction alopecia, which is also called traction alopecia. After exposure to radiation, hair follicle cells are damaged, resulting in temporary or permanent hair loss.

Chemical hair loss : Some chemicals may burn the scalp and cause hair loss when they come into contact with the scalp, such as hair perms and hair dyes. Drugs are a type of chemical substance, and some drugs can cause hair loss while treating other diseases.

Infectious hair loss : Infection by various pathogens is the main factor in hair diseases, mainly including infections by bacteria, viruses, fungi, spirochetes, parasites, etc. Seborrheic dermatitis and folliculitis are common scalp infection problems.

Immune alopecia : Patients with certain autoimmune diseases or immunodeficiency diseases will experience hair loss. Some are local immune diseases that occur in the hair, such as alopecia areata and alopecia universalis.

This concludes the introduction to the basic knowledge of hair in this issue. In the next issue, let us follow dermatologist Dr. Liu to learn about “common hair loss diseases”.