Melasma, Sun Spots, or Post-Acne Marks? How to Tell Them Apart

How can you tell melasma, sun spots, and post-acne marks apart?

All three are extra pigment where you would rather not have it. Trigger, pattern, edge, and timeline separate them, and one clinical review describes all three side by side ^[1].

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Built from Plensdorf 2017, Sathe and Launico 2026, Handel 2014, Davis and Callender 2010 and Praetorius 2014; last checked 2026-09.

What is melasma?

Melasma is an acquired pigment condition: symmetric brown-to-grey patches on sun-exposed facial skin, which in plainer terms means the cheeks, forehead, chin, and the skin above the upper lip ^[2][9].

Its causes stack on each other: sun exposure without burning is the most important single trigger ^[4], visible light adds to it ^[2], and hormones are the other half, since melasma commonly develops or worsens in pregnancy or on oral contraceptives, which is how it earned the nickname "the mask of pregnancy" ^[2][9].

Melasma is also chronic and relapsing, with no curative treatment ^[5]. The pregnancy-triggered form tends to fade after birth, so treatment is often postponed to let that happen ^[1], and melasma generally fades with age, disappearing in most women after menopause ^[5].

What is a sun spot?

A solar lentigo, known as a sun spot, age spot, or liver spot, is a flat, well-circumscribed spot running from light yellow to dark brown, often mottled, on the skin the sun reaches most ^[1][8]. They run from a few millimeters up to a centimeter or so ^[1][8], and despite the old name they have nothing to do with your liver beyond a similar color ^[8].

What a sun spot records is accumulated ultraviolet exposure: repeated UV drives a mild proliferation of pigment-making cells at the base of the epidermis along with more pigment ^[1], and lentigines follow sun exposure and photodamage ^[10]. Removal is a clinic conversation, with one review putting cryotherapy first line and topical therapy as an alternative or as maintenance afterwards ^[11].

How are freckles different from sun spots?

Freckles (ephelides) are smaller, 1 to 2 mm across, sharply defined, uniform in color, and they start in childhood ^[1]. The distinction is causal: ephelides are largely genetically determined though induced by sunlight, while lentigines come from sun exposure and photodamage ^[10]. Freckles also fade during the winter months, which a sun spot will not do ^[1].

What is a post-acne mark?

Post-inflammatory hyperpigmentation, usually shortened to PIH, is the flat dark mark left behind after skin has been inflamed or injured ^[3]. Its most useful feature is position: PIH appears in the same distribution as the inflammation that caused it, so the mark sits precisely where the pimple, bite, scratch, or burn was ^[3]. Acne is among the commonest causes and more frequent in deeper skin tones: in one 2002 study of acne in skin of color, acne-induced PIH developed in 65.3% of 239 African-American patients, 52.7% of 55 Hispanic patients, and 47.4% of 19 Asian patients ^[3].

Depth sets both color and timeline: pigment held in the epidermis reads tan to dark brown and may take months to years to resolve untreated, while pigment that has dropped into the dermis reads blue-grey and can be permanent ^[3][12].

What worsens PIH is more of what started it, which is why managing these marks begins with settling the underlying condition rather than attacking the pigment ^[3][12].

Why does it matter which one you have?

Each of the three answers to a different lever. Melasma wants photoprotection maintained indefinitely, with anything beyond that belonging to a clinician ^[2][5]. A solar lentigo is fixed photodamage, so prevention is what stops new ones arriving ^[11][14]. PIH is secondary by definition, so the first move is calming its cause ^[13][12]. Get the sorting wrong and you lose months, since an aggressive fading routine aimed at post-acne marks can irritate skin and prolong the mark it targets ^[3].

Two nearby complaints are worth separating out. If the issue is overall flatness rather than a defined mark, that is a different read: why skin looks suddenly dull. Under-eye darkness is its own question and not always pigment, which the pigmented-versus-vascular table takes on.

What helps all three?

Sun protection first, for all three ^{[1][3][5][13][14]}. The generic version: a broad-spectrum sunscreen, SPF 30 or higher, reapplied at least every two hours and more often when you are sweating or swimming, plus shade and cover-up ^[16][13]. In melasma it does double duty, preventing relapse and improving how well other treatments work ^[7].

Melasma has one extra complication: UVA and visible light pass through window glass and windshields, so a shaded room is not automatically a protected one ^[5], and in 20 volunteers with skin types IV to VI, visible light produced pigmentation that was darker and more sustained than pigmentation from long-wavelength UVA ^[6]. Ordinary UV filters do not block visible light, which is why melasma guidance favors a tinted sunscreen containing iron oxides ^[2][13]. We do not sell a sunscreen, and no antioxidant serum stands in for one; pick a dedicated SPF brand and wear it daily.

When should a dark spot be looked at by a dermatologist?

Earlier than most people assume, because what looks like an age spot can be a skin cancer, so a skin exam comes before any spot-fading project and treating a skin cancer as an age spot gives the cancer time to grow ^[14]. The differential for a solar lentigo includes lentigo maligna, and biopsy is indicated for rapid growth or change, pain, itching, easy bleeding, or anything atypical ^[1]. The plain rule: book an appointment for any spot that is new, different from your others, or changing, itching or bleeding, and for asymmetry, an irregular border, or color that varies from one area to the next ^[15][8]. Nothing here is a diagnosis, and melasma in particular is identified by a clinician.

Where does a vitamin C serum fit?

After the sunscreen conversation, as a supporting player. Vitamin C sits on the American Academy of Dermatology's list of over-the-counter ingredients for fading dark spots, alongside azelaic acid, glycolic acid, kojic acid, and a retinoid ^[13]. Ascorbyl tetraisopalmitate, an oil-soluble ester of vitamin C, has been studied on UVB-induced pigmentation at a research concentration, where it released vitamin C as a precursor and appears to work through antioxidant activity ^[17]. Which ingredient to reach for, and how vitamin C pairs with niacinamide, belongs with the red-versus-brown marks guide.

The ester holds up better than L-ascorbic acid and still degrades as an antioxidant under oxidative stress ^[18], and warmth sets the pace of that loss, as it does for degradation reactions generally ^[19]. A sun spot is a record of accumulated ultraviolet exposure ^[1], and an antioxidant serum keeps a similar record of every warm month it sat through before you opened it, which is why the batches of our own serum are made fresh weekly and kept refrigerated at about 4°C in the studio until the day they ship. The FDA requires every sunscreen label to tell you to protect the product from excessive heat ^[16]; a vitamin C serum obeys the same chemistry with no label required to say so, and what temperature does to an active over time is the longer argument.

Cryo-C, our oil-soluble vitamin C serum uses that ester in a waterless base of jojoba, rosehip, and squalane, with sea buckthorn and vitamin E. What we say about our own bottle stays where our evidence sits: skin looks brighter and glowier, and 69 of 159 written Cryo-C reviews mention glow or brightening. No serum erases a mark, and a topical fading routine of any kind runs on weeks and months of daily use ^[14]. Patch-test first if your skin is reactive, since irritation is itself a pigment aggravator ^[3], and note the light carrot seed and sweet orange scent; the protocol for adding anything new lives in the short list of steps a routine needs.