The Battle for Thinning Hair Terminal Hair vs. Vellus-like Hair
Believe it or not, your scalp is like a battlefield where two types of hair are constantly competing for space. When one side loses this battle, it can lead to hair thinning, one of the most common concerns among men worldwide.
Understanding the Two Types of Hair
The two types of hair involved in this battle are Terminal Hair and Vellus-like Hair. Both naturally exist on the scalp, but they differ significantly in structure and function.
Terminal Hair
This is the healthy, mature hair that everyone hopes to have. It is thick, strong, and fully developed, produced by healthy hair follicles functioning at their full capacity.
- Hair Follicle: Located approximately 3–5 mm beneath the skin. Contains a large dermal papilla with a rich blood supply.
- Hair Shaft: Thick, with a diameter of 60–100 microns or more. Well pigmented.
- Growth Cycle: Has a long Anagen (growth) phase lasting several years, allowing the hair to remain on the scalp for an extended period before naturally shedding.
Vellus-like Hair
This refers to hair that was once thick but has gradually become thinner through the process of follicular miniaturization.
- Hair Follicle: Positioned very close to the skin surface. Has a much smaller dermal papilla.
- Hair Shaft: Fine, with a diameter of less than 30 microns. Lightly pigmented or translucent.
- Growth Cycle: Has a short growth phase lasting only a few weeks, causing it to shed much more quickly.
The Balance Between Terminal Hair and Vellus-like Hair
Under normal conditions, both Terminal Hair and Vellus-like Hair are present on the scalp. Their proportions vary depending on genetics and the current health of the hair follicles.
- A Healthy Scalp: A healthy scalp should consist of more than 90% Terminal Hair, while Vellus-like Hair should account for less than 10% of the total hair population.
- When Scalp Health Declines: As scalp health deteriorates, the balance begins to shift. Thick, healthy Terminal Hair gradually decreases, while fine Vellus-like Hair occupies more of the scalp. As a result, the hair appears thinner because more of the scalp becomes visible.
image credit: Donovan Hair Clinic
How Does Vellus-like Hair Take Over the Scalp?
In reality, Terminal Hair gradually transforms into Vellus-like Hair through a process called follicular miniaturization. During this process, the hair becomes progressively finer, shorter, and lighter in color. If the follicle is still in the intermediate phase, it may still be possible to restore the hair and improve its strength.
However, once Terminal Hair has completely transformed into Vellus-like Hair, becoming thin, short, and fragile, treatment becomes much more challenging. If the follicle eventually reaches senescence, where the dermal papilla has been irreversibly damaged and can no longer produce new hair, it will no longer respond to treatment.
Understanding Androgenetic Alopecia
This concept helps explain androgenetic alopecia, commonly known as hereditary pattern hair loss.
Although androgen hormones stimulate Vellus-like Hair on areas such as the beard and chest to develop into Terminal Hair during puberty, these same hormones have the opposite effect on the scalp. In genetically susceptible individuals, they gradually transform Terminal Hair into Vellus-like Hair.
Therefore, hereditary hair loss does not occur because hair suddenly disappears. Instead, it is a gradual process in which Terminal Hair slowly miniaturizes into Vellus-like Hair over time.
Recognizing the Warning Signs of Hair Thinning
In clinical practice, specialists use magnified scalp examinations to assess the condition of the scalp and evaluate the proportion of Terminal Hair and Vellus-like Hair.
Terminal Hair : Vellus-like Hair > 7 : 1
Terminal Hair : Vellus-like Hair < 4 : 1
When the ratio falls below 4:1, it indicates that hair follicles are undergoing miniaturization and healthy terminal hairs are becoming finer and weaker.
This serves as an SOS signal from your hair follicles and scalp, indicating that it is time to seek appropriate treatment before Vellus-like Hair wins the battle for scalp coverage and the opportunity for recovery is lost.
Article by: Namnin Clinic | Hair and Scalp Physicians | Published: June 2026
