What causes pigmentation (dark patches) on the skin?

Pigmentation Is Not a Single Condition

The dark patch you see in the mirror is not one single disease. Darkening of the skin caused by melanin (hyperpigmentation) covers several distinct conditions: melasma, post-inflammatory hyperpigmentation, pigmentation due to long-term sun damage, ephelides (freckles), darkening of skin folds and dark circles around the eyes. The international consensus statement, which reflects the shared view of experts on this subject, does not treat these as a single problem; it lists each one as a separate condition and sets treatment according to the condition.

This article explains how pigmentation forms, not which product you should use. Three situations are the most common on the face: damage the sun builds up over the years, melasma, which is sustained by hormones and light acting together, and the mark left behind by inflammation. All three use the same pigment, melanin, but they build it up for different reasons, in different layers and with different degrees of persistence.

In practice, this distinction means that the three conditions do not respond in the same way to the same protection, the same skincare or the same procedure. So the first step is not to erase the pigmentation but to understand what type it is.

Where Melanin Is Made and How It Spreads

Melanin is made in cells called melanocytes, which sit in the bottom row of the epidermis (the outer layer of the skin). Production takes place in small sacs inside these cells, called melanosomes, and the key enzyme in the process is tyrosinase. This is why, among the active ingredients applied to the skin to reduce pigmentation, those that target this enzyme are still widely used.

A melanocyte does not keep the pigment it makes. Melanosomes are passed through the cell’s projections to the surrounding keratinocytes, the main cells of the epidermis, and that is where the visible colour of the skin is actually formed. So what we call pigmentation is often not a change in the number of melanocytes but a change in the amount, type and distribution of the pigment they produce.

Production is not simply switched on and off; it is controlled by signalling pathways that work through regulatory proteins (transcription factors) such as MITF. Ultraviolet light, hormonal signals, oxidative stress and inflammation can each affect these pathways separately. According to research on melasma, many different factors converge on the MITF axis, oxidative stress cycles and nerve-hormone (neuroendocrine) pathways and keep the melanocyte constantly active. In other words, pigmentation is the result not of a single stimulus but of overlapping stimuli.

Colour Is Not Set by Melanocytes Alone

For a long time, pigment disorders were viewed only through the melanocyte. Current research is widening this view. The tissue environment the melanocyte sits in directly affects pigment production: neighbouring keratinocytes, fibroblasts (the cells that make collagen) in the connective tissue of the deeper layer (the dermis), mast cells and blood vessels. For this reason, pigment problems are now approached not only in terms of melanin production but together with the melanocyte’s whole tissue environment.

It is reported that fibroblasts in the dermis release substances that both increase and reduce pigmentation, and that the supporting tissue between cells (the matrix) can change the melanocyte’s tyrosinase activity and the transfer of melanosomes. The release of substances that increase pigmentation is also reported to be higher in melasma and in sun spots (solar lentigines).

What this means for you is this: an approach that targets only the melanocyte addresses only part of the picture. Part of the stubbornness of pigmentation comes from this.

How Sun Spots Form

Dark spots with fairly well-defined edges that gradually appear on areas exposed to the sun for many years (the backs of the hands, the forearms, the outer parts of the face, the décolletage) are part of photoageing (sun-related skin ageing). According to research, long-term sun exposure accounts for the largest share of the external factors that age the skin; this ageing shows up as discolouration as well as wrinkles.

The mechanism here is not a one-off burn but accumulation. Repeated ultraviolet exposure both stimulates the melanocyte and changes the tissue around it; changes in the dermis have been reported to send signals back to the pigment-producing cell. This is why a sun spot is the mark not of a single summer but of year after year. People with darker skin (darker phototypes) are reported to be more prone to discolouration; the role of light protection in reducing the risk of these changes is also addressed separately.

Ephelides, commonly known as freckles, are covered under a separate heading in the international consensus statement. Although they look similar, they are considered a different group from spots caused by long-term sun damage. Putting the two in the same category based on appearance alone is the first step towards the wrong plan.

Why Melasma Is Stubborn

Melasma is a long-lasting (chronic) condition that tends to recur and usually appears as symmetrical brown patches on the face. It is more common in women and has no single cause; it is described as a disease in which many factors play a part together.

According to research into the causes of melasma, internal and external factors work together. On one side are hormone levels, oxidative stress, thyroid dysfunction, vitamin D metabolism and psychological stress; on the other are ultraviolet light, visible light, air pollution, some medicines, diet and skincare habits. These factors are reported to meet in shared signalling pathways and keep the melanocyte in a constantly stimulated state.

The second issue is depth. Melasma has been shown not to be limited to the outer layer (the epidermis). Examinations of skin affected by melasma have found the following changes:

• Damage to the membrane that separates the outer and deeper layers (the basement membrane).
• Melanocytes hanging down into the deeper layer (the dermis).
• Marked sun-related damage to elastic fibres (solar elastosis).
• More pigment-engulfing cells (melanophages) and mast cells.
• Formation of new blood vessels.

In other words, part of the condition lies beneath the surface.

The third issue is recurrence. Research indicates that conventional approaches that target pigment that has already formed have a high recurrence rate, and that these approaches deal with the result rather than the cause. This is why strict light protection is considered fundamental in melasma: trying to remove the pigment while the trigger is still present means ending up back where you started.

How Marks Remain After Inflammation

Post-inflammatory hyperpigmentation is extra pigment that the skin leaves in an area after inflammation there. The trigger can be acne, eczema, an allergic reaction, friction, a burn or a procedure performed on the skin. Whatever the trigger, the mechanism is the same: inflammation stimulates the melanocyte, and the pigment produced stays in the outer layer (the epidermis) and sometimes in the deeper layer (the dermis).

This type of pigmentation is more common and more noticeable in darker skin. Research indicates that the marks can last a long time and that the psychological and social burden they place on a person should not be underestimated. A consensus statement on acne-related marks points out an important detail: marks can develop even in mild and moderate acne, without obvious signs of inflammation. So a mark can still be left even when there is no visible redness. Innate immune responses, the skin flora (the microorganisms that live on the skin) and external factors such as ultraviolet light, visible light and air pollution are also reported to contribute to the condition.

The data on prevention do not support strong claims. A review that brought together studies on preventing this pigmentation in darker skin found that, of the measures tested, only sun protection worked consistently; the other measures can reduce its severity rather than prevent it completely. Almost all of the cases examined were reported after energy-based procedures, and the face was the most frequently reported area, so the results cannot be applied directly to every type of procedure. What can be generalised is this: darker skin is more prone to post-inflammatory hyperpigmentation, and this should be raised in advance whenever any procedure on the skin is being discussed.

Beyond Ultraviolet: Visible Light

For a long time, sun protection was discussed only in terms of ultraviolet light. In recent years, the role of visible light, especially its blue end, in pigmentation has become clearer. According to research, visible light makes up almost half of the radiation that comes from the sun; its high-energy part contributes to redness, persistent pigmentation and photoageing, and acts together with long-wavelength ultraviolet A.

Its mechanism differs from that of ultraviolet light. Visible light is reported to increase MITF through a light-sensitive protein in the melanocyte called opsin-3, leading to the formation of more stable melanosomes that resist breakdown. This is one of the mechanisms that explain why pigment lasts longer in darker skin.

The practical consequence is this: protection that filters only ultraviolet light may not give the expected benefit in melasma or post-inflammatory hyperpigmentation. For protection against visible light, the option with the most data behind it is tinted formulations containing pigments such as iron oxide. However, the sources also add a caveat: because of colour-matching and texture issues, these products can be hard to use regularly in daily life, and protection that is not used does not protect.

Why Pigment Depth Matters

One of the first questions to ask when looking at a patch of pigmentation is where the pigment sits. Pigment that builds up in the outer layer (the epidermis) is not the same as pigment that has moved down into the deeper layer (the dermis) and is carried inside pigment-engulfing cells (melanophages).

The international consensus statement groups treatment options according to the subtype of the condition and the depth of the pigment; in other words, depth is not a detail but a factor that shapes the plan. In melasma, a component that extends into the deeper layer has been demonstrated; this means that part of the condition sits where methods acting from the surface cannot reach.

Depth is assessed at the consultation. In melasma, diagnosis is reported to be made mainly by clinical examination, and a Wood’s lamp (an examination using a special light) and dermoscopy (examining the skin under magnification) can support this assessment. These are supporting tools; they do not provide a definitive map of the layers. This is why, for any type of pigmentation, no time frame can be promised at first glance; a promised time frame is based on guesswork, not on scientific data.

Why the Three Conditions Are Not Managed the Same Way

The international consensus statement does not reduce the treatment of pigmentation to a single formula. It proposes decision pathways that vary according to skin type, the depth of the pigment, the severity of the condition and access to treatment in the region. This points to something important: the right step comes from the diagnosis, not from the procedure.

With sun-related pigmentation, the main issue is accumulated damage; any intervention carried out before sun protection is properly in place ends up back at the same point. Melasma is chronic and its triggers persist; an approach that targets only pigment that has already formed has been reported not to prevent recurrence. With post-inflammatory hyperpigmentation, the main task is to bring the inflammation that triggers it under control; as long as the underlying acne or dermatitis (skin inflammation) continues, new marks keep appearing.

All three conditions share the same basis: broad-spectrum protection that covers the whole ultraviolet range and visible light. In scientific sources, this protection is seen not as one treatment step but as the foundation on which everything else is built. The conditions differ in what is added on top of this foundation, and that is a matter for a consultation, not an article.

Not Every Dark Spot Is Benign

This warning is especially important: the three conditions described above are benign, but not every dark area that appears on skin with long-term sun exposure is one of these three conditions.

Lentigo maligna and lentigo maligna melanoma are subtypes of melanoma (a type of skin cancer) linked to long-term sun exposure, and they often occur on areas such as the face and neck. Research clearly states that these lesions are difficult to diagnose early because they look like benign conditions. It is reported that the diagnostic accuracy of naked-eye examination, dermoscopy and reflectance confocal microscopy (an imaging method that does not involve cutting the skin) has not been established with certainty in comparison with examination of a tissue sample (histopathology). In other words, a decision based on looking at a spot is not enough on its own.

Research on head and neck melanoma completes the picture: melanoma in this area occurs at an older age and more often on skin with long-term sun exposure, varies in appearance and has a worse outlook than melanoma on other parts of the body.

In practice, the threshold is this: a spot that is new, is growing, has edges that are becoming irregular, shows different colours within it, itches, bleeds or looks different from the other spots on your skin is not a cosmetic problem. With such a spot, the next step is a dermatological assessment; a diagnosis must be made before any aesthetic plan is considered. Trying to lighten a spot that has not been diagnosed is the quietest way to delay its diagnosis.

Pigmentation Treatments Offered Here

The clinic offers skin mesotherapy and skin rejuvenation treatments, and pigmentation is one of the concerns assessed in these treatments. The consultation identifies which condition is the main one (accumulated sun damage, melasma or the mark left by past inflammation), and the order of the steps is set accordingly. You can read about the scope and limits of these treatments on the Pigmentation Mesotherapy and Skin Rejuvenation pages.

This page cannot tell you which condition you have; it only explains how the conditions differ from one another. That distinction is made at a consultation. After reading, you decide what to do next.