What is pigmentation?

All skin colour (pigment) is a result of melanin, two different substances produced by specialised cells in the skin called melanocytes. Melanin functions to protect skin by absorbing and dissipating UV radiation, thereby preventing free radical formation and skin damage. Melanin is essentially our natural sunscreen (fun fact: it has an SPF of 3.4, meaning it absorbs about 50-75% of UV light hitting the skin).

Melanocytes are found in the basal (deepest) layer of the epidermis. They synthesise and package melanin inside the cell using an enzyme called tyrosinase and transfer the melanin-containing package (called a melanosome) to between 30 and 40 neighbouring skin cells (keratinocytes) using finger-like extensions called dendrites. These is how melanin is distributed throughout all layers of the epidermis.

Melanin produces all pigment in normally functioning skin and hair, but mottled brown patches of pigmentation (called hyperpigmentation) are aesthetically displeasing, and usually one of three types:

1. Photo-ageing related pigmentation: caused by exposure to UV light.

2. Melasma: a complex pigmentary disorder thought to involve a hormonal influence, but triggered by UV exposure.

3. Postinflammatory hyperpigmentation (PIH): caused by trauma (injury or inflammation) to the skin, particularly in people with darker skin tones.

Pigmentation makes us look older!

Cosmetically, we don’t like looking at our own patchy skin tone in the mirror, but there is evidence that points to hyperpigmented skin being assessed as ‘older’ than an even skin tone.

Multiple experiments have concluded that 3D simulated faces (both male and female), standardised to vary only in skin colour distribution (i.e. even skin tone vs pigmentation), signalled youth, health and attractiveness when they have an even skin tone versus mottled appearance due to age and UV induced photodamage. This was completely independent of wrinkles, skin laxity and loss of facial volume, all things that are typically considered ‘ageing’.

Photoaging and UV induced pigmentation

When melanocytes are exposed to UV, they upregulate the enzymes involved in melanin synthesis and transfer more melanosomes to more skin cells. UV also damages melanocyte DNA, resulting in increased melanin synthesis. The skin cells themselves also respond to UV radiation by taking up more melanosomes, and producing inflammatory chemicals.

All of this results in pigmentary changes in the skin. Aged skin that has been protected from the sun is pale and wrinkled, but generally with regular, not irregular, pigmentation – think about the skin on your torso that doesn’t see as much sun vs the skin on your arms, chest, face and hands (check out the image if that’s not frightening enough for you!).

Note: Photoaging from chronic UV exposure is really a minor cosmetic concern, although it can significantly affect our self-confidence. The much larger concern with UV damage is DNA damage caused by UV radiation – if this exceeds our cells’ own DNA repair mechanisms, it results in mutations and immune system changes that are the basis of skin cancer and melanoma development.

Melasma

Melasma is patchy brown hyperpigmentation that occurs on sun-exposed areas of the face. It can also appear on the neck and arms, usually in post-menopausal women. You may have heard it called ‘the mask of pregnancy’ because it often appears in pregnancy, however oral contraceptives and hormone replacement therapy can also be involved. Sun exposure is a major triggering and aggravating factor.

Melanocytes contain oestrogen receptors, so it is thought that the melanocytes in people with melasma are more sensitive to the stimulatory effects of oestrogens. This results in larger melanocytes that produce and transfer more melanosomes to keratinocytes, resulting in hyperpigmented patches.

Unlike UV-induced hyperpigmentation which appears as random patches, melasma appears in one of 3 patterns:

1. Centrofacial (most common): a symmetrical pattern on forehead, cheeks, upper lip, nose and chin

2. Malar: the cheeks and nose

3. Mandibular: the jawline

Melasma is a frustrating and emotionally distressing disorder as it is chronic and often relapses, especially with continued sun and hormone exposure.

Post-inflammatory Hyperpigmentation

PIH is a reaction to injury or inflammation that causes the skin to produce increased pigment. It is more common in darker-skinned individuals. The most common cause of PIH is acne, but it also can result from psoriasis, a burn, or any skin injury.

PIH results from a local overproduction of melanin and appears as dark spots/patches in the same area as the healed injury. These marks can take several months to years to resolve, even with treatment. And they may worsen with exposure to UV. This is why PIH is THE major reason you shouldn’t pick at your face, and wear sunscreen if you suffer from breakout-prone skin!