During puberty, some vellus hair changes to thicker hair called terminal hair.
In this article, we look at how vellus hair changes over time, as well as how it is related to health and hair loss.
What is vellus hair?
Vellus hair develops in infancy and finer than terminal hair.
Vellus hair is the light, short, fine hair that covers much of a person's body. Its length and thickness will vary from person to person. The primary role of vellus hair is to protect the skin and keep the body warm.
Terminal hair, on the other hand, is the longer, thicker, and darker hair that grows on the head. It also forms the thick patches of body hair in the pubic region, under the arms, and beard.
Terminal hairs may appear on other parts of the body, particularly after puberty. It is normal to find a few longer, thicker strands of hair in an area primarily covered with vellus hair.
People who lose terminal hair usually still have vellus hair. This is why men who are experiencing male pattern baldness might still have fine, light patches of hair on their head. Vellus hair is sometimes more noticeable on women and children than men because males tend to have more terminal body hair.
The thickness, color, and length of vellus hair will vary between individuals. In some people, vellus hair is only visible in bright natural light and at a close distance. Other people have slightly thicker and darker vellus hair that may be more noticeable. Some areas of the body may have thicker vellus hair than others.
Vellus hair has a similar structure to terminal hair. Both types of hair grow from a hair follicle. Each hair follicle contains a gland that secretes sebum, an oil that lubricates the skin and hair.
However, unlike terminal hair, vellus hair does not typically have a medulla. The medulla is a portion of the hair's core that strengthens it, allowing it to grow longer.
Vellus versus lanugo
Lanugo is a type of hair that develops on a fetus while it is still in the womb. It protects the skin from amniotic fluids and is usually shed before or shortly after birth.
Babies born prematurely tend to have more lanugo than babies born at full gestation. Some babies have thicker or darker lanugo than others. In all babies, vellus hair eventually replaces the lanugo.
Vellus and terminal hairs follow identical growth patterns. The three phases of hair growth for both types of hair are:
- Anagen: The period of active hair growth, during which the hair grows longer. Vellus hair tends to have a shorter anagen phase than terminal hair.
- Catagen: A period of transition, during which the hair follicle contracts and limits blood supply. The hair can easily fall out during this stage.
- Telogen: A resting period during which the hair does not grow.
Everyone will have hairs in all three stages of development at any one time. This is why some hair may regrow immediately after being plucked, but other hair may take months or even years to return.
How much is normal?
Vellus hair can alter as we age and the amount does not usually reflect a person's health.
The amount of vellus hair varies between individuals and can also change according to age and hormonal shifts.
In some people, the vellus hair is more visible because of its color or because of the color of the person's skin, making it appear like they have significantly more vellus hair than others. In others, the vellus hair grows longer, making the hair more visible.
Having more or less vellus hair does not necessarily reveal anything about a person's health. However, some hormonal conditions can cause vellus hair to become terminal hair, such as in males during puberty.
Certain medications, including chemotherapy drugs, may cause terminal hair to fall out or become vellus hair.
Vellus hair tends to get shorter as a person ages, making it appear as though a person has less hair than they used to. However, the quantity of vellus hair does not vary significantly between the sexes.
Vellus hair and terminal hair
Vellus hair follicles are no different from other hair follicles. In fact, many hair follicles transition from vellus to terminal, and sometimes back again. During puberty, androgens—hormones such as testosterone—cause some vellus hairs to transition to terminal hairs.
In men and some women, for example, many of the vellus hairs on the neck and cheeks become terminal hair that forms the beard.
People who experience hair loss can see their hair transition from terminal hair back to vellus hair. In some cases, it may be possible for the hair to become terminal hair again.
Baldness and vellus hair
The hormone Dihydrotestosterone can cause male pattern baldness in both men and women.
The most common form of hair loss, male pattern baldness, can affect both men and women. This type of baldness occurs when a hormone called Dihydrotestosterone (DHT) attacks the hair follicle. This hormone weakens the hair, causing it to turn thin and brittle, and eventually fall out. If hair regrows, it may be weaker vellus hair rather than terminal hair.
Many treatments for baldness attempt to convert vellus hair back to terminal hair by preventing DHT from attacking the hair.
Increasing blood flow to the hair follicle may also help, as blood flow is vital for hair growth. Some forms of baldness decrease blood flow, causing terminal hair to become vellus hair.
Vellus and terminal hair are just two different forms of the same hair growth pattern. The same follicles produce these hairs, as well as the lanugo that many babies are born with.
Most changes in hair growth are harmless, but might be a cosmetic concern for some people. A variety of changes can alter the way hair grows, so people who notice a sudden increase in vellus hairs should talk to their doctor.
A doctor can help a person understand the change and offer options for addressing unwanted hair growth or baldness.