Sun spot, melasma or acne mark: how to tell them apart

A brown spot on the face always looks like the same thing in the mirror. It is not. Beneath the same dark tone there can be very different processes: years of accumulated sun, skin with a hormonal and genetic tendency to produce pigment, or the mark a spot left behind as it became inflamed. And the difference is not academic. What lightens a sun spot may worsen melasma, and what resolves an acne mark in months may be useless on a spot that is ten years old.

This article explains how to tell apart the three most frequent facial dark spots, what causes them, how they develop and why treatment changes depending on the type. It also explains the most important point: which spots should not be treated without a prior medical assessment.

Why dark spots appear: the same pigment, different causes

Skin colour depends mainly on melanin, a pigment produced by melanocytes, cells located in the basal layer of the epidermis. Each melanocyte distributes pigment to dozens of neighbouring cells, the keratinocytes, which use it like a parasol over their nucleus.

A dark spot (hyperpigmentation) arises when there is more melanin in one area than around it. This can happen by three main routes:

• More melanocytes, or melanocytes that are permanently more active, in a limited area, as happens in a solar lentigo after years of ultraviolet radiation.
• Melanocytes that overreact to various stimuli (sun, visible light, heat, hormones), on a predisposed genetic background, as in melasma.
• A response to inflammation: when the skin becomes inflamed, inflammatory mediators stimulate the melanocytes. This is what happens after a spot, a burn, eczema or an overly aggressive treatment.

There is another detail that greatly changes the prognosis: the depth of the pigment. Melanin can remain in the epidermis (more superficial, brown, better response to treatment) or drop into the dermis (deeper, greyish or bluish tone, much more persistent). At the consultation, examination with a dermatoscope and Wood's lamp helps to work out where the pigment is, although many spots are mixed.

Finally, not every spot that looks brown is pigment. Some acne marks are red or purplish because of dilated vessels, and that requires a completely different approach.

Sun spot (solar lentigo): the record of accumulated sun

The solar lentigo, also called senile lentigo or "age spot", is the most common spot on sun-aged skin. It has nothing to do with age itself, but with the ultraviolet radiation accumulated over decades.

How to recognise it:

• Light to dark brown spots, uniform in colour, flat.
• Well-defined borders, a round, oval or slightly irregular shape.
• Variable size, from a few millimetres to more than a centimetre.
• Located where the sun hits most: cheekbones, temples, forehead, nose, backs of the hands, décolletage and forearms.
• They usually appear from the age of 40, earlier in people with a lot of exposure or sunburn.
• They do not disappear in winter, unlike freckles.

Lentigo or freckle? Freckles (ephelides) appear in childhood, in people with fair skin, are small and numerous, darken in summer and fade in winter. A lentigo appears later and stays all year round.

Why it matters: a solar lentigo is benign. But it is also a marker of cumulative sun damage, which means the surrounding skin has had enough exposure to justify monitoring. And there are lesions that look like a lentigo and are not. The most important is lentigo maligna, a form of melanoma in situ that arises precisely on the face of older people with a lot of accumulated sun, and which at the start may look like "just another spot". Dermoscopy helps tell these lesions apart: lentigo maligna tends to show asymmetric pigmentation around the follicles, grey dots and globules and rhomboidal structures, signs that are not expected in a solar lentigo.

Other lesions that can be confused: flat seborrhoeic keratosis (which over time becomes raised with a rough surface) and pigmented actinic keratosis (rough to the touch, potentially pre-malignant).

Response to treatment: because the pigment is mainly epidermal and well defined, a lentigo usually responds well to targeted treatments. But only once the diagnosis has been confirmed.

Melasma: the patch that responds to sun, light and hormones

Melasma (also called chloasma, especially when it appears in pregnancy) is a chronic, recurrent hyperpigmentation. It is far more common in women, especially between the ages of 20 and 50, and in intermediate and darker skin phototypes. It also affects men, to a lesser extent.

How to recognise it:

• Brown spots, sometimes greyish, with irregular, "map-like" borders.
• Symmetrical distribution, on both sides of the face.
• Three typical patterns: centrofacial (forehead, nose, upper lip, chin), the most common; malar (cheekbones); and mandibular (along the jawline).
• The upper lip in a "moustache" pattern is highly suggestive.
• Worse in summer and partly better in winter, but rarely disappears.

What causes it: melasma has no single cause. The most consistent factors are:

• Genetic predisposition. In an international survey of women with melasma, around half had first-degree relatives with the same condition.
• Ultraviolet radiation, the main aggravating factor.
• Visible light, especially short-wavelength light (blue-violet), which stimulates pigment for longer in darker skin. That is why ordinary sunscreen, which mainly filters UV, is not always enough.
• Hormones: pregnancy, oral contraceptives, hormone therapy. Many women notice the onset or worsening in one of these phases.
• Heat, which seems to worsen pigmentation in some people.
• Changes in the dermis itself: the most recent research shows that skin with melasma has signs of sun damage (elastosis), more vessels and changes in the basement membrane. That is why several authors now describe melasma as a photoageing disease, and not just an excess of pigment.

Why it is hard to treat: melasma is chronic. It can lighten a great deal with treatment and rigorous protection, but tends to return with the summer sun, with heat or with hormonal changes. And there is a specific risk: aggressive treatments (some lasers, deep peels, excessive heat) can inflame the skin and worsen the patch, or cause "rebound" hyperpigmentation. That is why melasma calls for a long-term, gentle strategy, and not a single intense treatment.

Acne mark: brown or red makes all the difference

When a spot disappears, it often leaves a flat mark where it was. Many people call it a "scar", but in most cases it is not: a true scar changes the contour of the skin (it is sunken or raised), whereas a mark is only a change in colour and can disappear completely.

There are two types of flat mark, and it is worth telling them apart.

Post-inflammatory hyperpigmentation (brown)

• Brown spots, from light brown to almost black, in the exact place of previous spots.
• Shape and size similar to those of the lesion that gave rise to them.
• Irregular, asymmetric distribution, following the acne (face, but also back and chest).
• Much more frequent and long-lasting in darker skin. In a classic study of acne in skin of colour, more than half of Black and Hispanic patients had post-inflammatory hyperpigmentation, and many found the marks more bothersome than the spots themselves.
• Made worse by the sun and by the habit of squeezing or picking at spots.

Post-inflammatory erythema (pink or red)

• Pink, red or purplish marks, more visible on fair skin.
• It is not pigment: they are small dilated vessels that remained after the inflammation.
• Simple test: press the mark with a clear glass or with your finger. If the colour blanches under pressure and returns when you release, it is mainly vascular. If it stays brown, it is pigment.
• Pigment-lightening agents are of little use here. When it persists, the options are different (treatments aimed at the vessels, on medical advice).

The good news and the condition

Both marks tend to fade on their own, within months, sometimes more than a year on dark skin. But there is one condition: the acne has to be controlled. While spots keep appearing, new marks keep appearing, and no lightening agent keeps pace with that. Treating the acne is the first treatment for acne marks. The second is daily sunscreen.

If the mark changes the surface of the skin (a hole, a depression or a raised area), we are no longer talking about a mark but a scar, which requires a different approach.

Comparison table: the three spots side by side

Other spots that can be confused

Not all brown spots on the face fit into these three categories. Some of the most frequent:

• Freckles (ephelides): small, numerous, present since childhood, varying with the seasons.
• Seborrhoeic keratosis: starts flat but becomes raised with a "stuck-on", rough surface. Benign.
• Pigmented actinic keratosis: rough, in highly exposed areas. It can progress to carcinoma and should be treated by a doctor.
• Hyperpigmentation from medicines or photosensitisation: some drugs and perfumes applied to the skin before sun exposure can leave marks.
• Naevi (moles): they can be flat and brown; they need monitoring, like any mole.
• Lentigo maligna and melanoma: rare, but the main reason to see a doctor before treating a spot.

Because treatment changes depending on the spot

There is a common basis for all three types: daily sunscreen, all year round. Without it, any lightening treatment loses its effect after a few weeks of exposure. From there, the strategies diverge.

Sun spot

• Because it is well defined and superficial, it responds well to treatments aimed at the spot itself, decided by the doctor after confirming that it is benign.
• Topical care (retinoids, vitamin C, niacinamide, exfoliating acids) helps even out overall tone and soften mild dark spots, but has a limited effect on well-formed lentigines.
• Superficial to medium chemical peels can help when there are several dark spots and diffuse photoageing.
• Treating does not prevent new spots: sun protection is what stops the next ones appearing.

Melasma

• Extended protection: broad-spectrum sunscreen with filters that also block visible light. In practice, this means tinted sunscreens, which contain iron oxides. In a randomised trial, a sunscreen with additional protection against visible light reduced melasma more than a UV-only sunscreen, and another study showed fewer relapses in summer with this type of protection.
• Topical lightening agents: hydroquinone has for decades been the most studied lightening agent, alone or in a triple combination with a retinoid and a low-potency corticosteroid. In the European Union it is banned in cosmetics and may only be used on medical prescription, for limited periods and with monitoring, because of the risk of irritation and, with prolonged use, of ochronosis (paradoxical darkening). Alternatives with variable evidence: azelaic acid, kojic acid, niacinamide, topical tranexamic acid, cysteamine, arbutin, retinoids.
• Oral tranexamic acid: there are randomised trials showing benefit in moderate to severe melasma, but it is an off-label use and has important contraindications, notably a history of thrombosis, some hormonal contraceptives and smoking. Only on medical decision and monitoring.
• Peels: they can help as a complement, provided they are superficial and the skin is properly prepared. Aggressive peels increase the risk of worsening.
• Lasers and pulsed light: irregular results and a risk of worsening and relapse; they are reserved for selected cases, always combined with topical therapy.
• Realistic expectation: to control, not to cure. Maintenance is permanent.

Acne mark

• First, the acne. Treatments such as topical retinoids and azelaic acid have the advantage of treating acne and lightening marks at the same time.
• Do not squeeze: picking at spots increases inflammation and, therefore, the mark.
• Gentle lightening agents (niacinamide, azelaic acid, vitamin C) and superficial peels can speed up lightening, with extra caution on darker skin.
• Red marks: lightening agents help little; if they persist for many months, the doctor may propose treatments aimed at the vessels.

Common mistakes that worsen any spot

• Scrubbing with grain scrubs or brushes.
• Applying acids or retinoids at high concentrations without adaptation, irritating the skin.
• Using lightening products bought outside regulated channels, which may contain potent corticosteroids or mercury.
• Treating the spot and forgetting sunscreen, or applying it in insufficient quantity and without reapplying.

When the spot should be seen by a doctor first

Before any aesthetic treatment, a spot should be examined by a doctor if:

The ABCDE rule (Asymmetry, Border irregularity, Colour variation, Diameter greater than 6 mm, Evolution) is a good aid for moles and spots, but it does not replace examination with a dermatoscope. Treating a suspicious spot with a laser or peel without a diagnosis may delay the detection of a melanoma.

It is also worth seeking assessment when:

• Suspected melasma, to define a safe long-term plan.
• The spots appeared after starting a new medicine.
• Acne marks do not improve after six months with the acne controlled.

At Luxmed, the skin consultation always begins by identifying the type of spot. Only then is the plan defined: home care, sun protection suited to your skin type and, if it makes sense, in-clinic treatments. If the spot raises doubts, it is referred for medical assessment before any treatment.

This article is for information purposes and does not replace a consultation. The results of any treatment vary from person to person.

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