Vitiligo

Vitiligo, likely meaning blemish, is a non-contagious skin condition that is defined by patches of discoloration, or depigmentation.

Though vitiligo can affect any race or ethnicity, it tends to be most noticeable in people with darker skin, like Canadian fashion model Winnie Harlow.

Given the effect on a person’s appearance, pigment loss can really impact a person’s quality of life.

The skin is divided into three layers--the epidermis, dermis, and hypodermis.

The hypodermis is made of fat and connective tissue that anchors the skin to the underlying muscle.

Just above is the dermis, which contains hair follicles, nerves and blood vessels.

And just above, the outermost layer of skin, is the epidermis.

The epidermis itself has multiple cell layers that are mostly keratinocytes - which are named for the keratin protein that they’re filled with.

Keratin is a strong, fibrous protein that allows keratinocytes to protect themselves from getting destroyed when you rub your hands through the sand at the beach.

Keratinocytes start their life at the deepest layer of the epidermis called the stratum basale, or basal layer, which is made of a single layer of small, cuboidal to low columnar stem cells that continually divide and produce new keratinocytes that continue to mature as they migrate up through the epidermal layers.

But the stratum basale also contains another group of cells - melanocytes, which secrete a protein pigment, or coloring substance, called melanin.

Melanin is actually a broad term that constitutes several types of melanin found in people of differing skin color.

These subtypes of melanin range in color from black to reddish yellow and their relative quantity and rate at which they are metabolized define a person’s skin color.

When keratinocytes are exposed to the sun, they send a chemical signal to the melanocytes, which stimulates the melanocytes into making more melanin.

The melanocytes move the melanin into small sacs called melanosomes, and these get taken up by newly formed keratinocytes, which will later metabolize the melanin as they migrate into higher layers of the epidermis.

Melanin then acts as a natural sunscreen, because its protein structure dissipates, or scatters, UVB light--which if left unchecked can damage the DNA in the skin cells and lead to skin cancer.

Melanocytes can also be found in the dermis, at the base of the hair follicle, and in the eye where they help color hair and the iris.