Spots on your skin usually come from one of a handful of common causes: sun exposure, hormonal changes, leftover marks from inflammation, aging, or less commonly, a nutritional deficiency or autoimmune condition. Most skin spots are harmless, but certain features can signal something worth getting checked. Understanding what’s behind yours starts with looking at the color, texture, location, and how quickly the spot appeared.
Sun Damage and Age Spots
The most common reason for dark spots is cumulative sun exposure. When ultraviolet light hits your skin, it triggers a chain reaction inside pigment-producing cells called melanocytes. UV photons directly affect your DNA, ramping up production of the enzyme responsible for making melanin. At the same time, surrounding skin cells release a cocktail of growth signals that tell melanocytes to multiply, produce more pigment, and resist dying off. Over years, this process creates flat brown patches known as solar lentigines, or what most people call age spots or sun spots.
These spots tend to show up on areas that get the most sun: the backs of your hands, your forearms, face, chest, and shoulders. They’re flat, tan to dark brown, and have relatively clear edges. Early sun exposure in childhood and adolescence accelerates their development later in life, making them resemble other pigmentation conditions like melasma or post-inflammatory marks.
Hormonal Spots and Melasma
If you’re seeing larger, patchy areas of brown or blue-gray discoloration, especially on your cheeks, forehead, upper lip, or arms, hormonal changes may be the driver. Melasma is one of the most common hormone-related pigmentation conditions, and it disproportionately affects women. Estrogen stimulates melanocytes to multiply and prompts surrounding skin cells to release pigment-boosting signals. Progesterone amplifies the effect by increasing both the number of melanocytes and the activity of the key enzyme that produces melanin.
Pregnancy, hormonal birth control, and hormone replacement therapy are all well-established triggers. Even medications that alter estrogen levels indirectly, like certain breast cancer treatments, have been linked to melasma development. Sun exposure on top of hormonal changes makes the patches significantly darker and harder to fade, which is why melasma often worsens in summer.
Marks Left by Inflammation
Dark spots that appear exactly where you had a pimple, a bug bite, a burn, or a rash are called post-inflammatory hyperpigmentation. After your skin heals from any kind of irritation or injury, excess melanin can pool in the area, leaving behind a flat discolored mark that ranges from tan to dark brown. These are not scars, though they often get mistaken for them.
How long they last depends on how deep the pigment sits. Surface-level marks that look tan or brown typically take months to fade on their own, sometimes longer. Deeper pigment that appears blue-gray can stick around for years or, in some cases, become permanent without treatment. Starting treatment early helps speed things up and prevents the spots from darkening further. People with darker skin tones are more prone to post-inflammatory hyperpigmentation and tend to see it last longer.
Benign Growths That Come With Age
Seborrheic keratoses are the waxy, slightly raised, “stuck on” looking growths that become increasingly common as you get older. They range from light tan to nearly black and can appear almost anywhere on the body. A study tracking their prevalence found they affected 12% of people aged 15 to 25, but 100% of people over 50. If you’re middle-aged or older and noticing new bumpy, well-defined spots with a rough or waxy surface, these are the most likely explanation.
They’re completely benign. The key feature that sets them apart from precancerous spots is their appearance: seborrheic keratoses have well-defined margins and look like they’ve been pasted onto the skin, while precancerous actinic keratoses feel rough and scaly, have blurry edges, and often appear as reddish patches that you can feel before you see them. Actinic keratoses show up almost exclusively on sun-exposed areas and can thicken over time.
White Spots and Vitiligo
Not all skin spots are dark. If you’re noticing milky-white patches where your skin has lost its color entirely, vitiligo is a possibility. This is an autoimmune condition where the body’s immune system attacks its own melanocytes, leaving behind depigmented areas. The patches most commonly appear on the hands, feet, arms, and face, though they can develop anywhere.
The most telling pattern is symmetry. Vitiligo patches typically show up on both sides of the body in matching locations, like both knees or both hands. A less common form affects only one side or one segment of the body. In some cases, the color loss happens gradually. In others, it can spread rapidly to cover large areas. Hair growing in affected patches may also turn white.
Nutritional Deficiencies
Vitamin B12 deficiency is one of the more underrecognized causes of skin discoloration. The most common sign is hyperpigmentation concentrated on the face, the creases of your palms, and skin folds. It can look strikingly similar to other pigmentation disorders. Interestingly, B12 deficiency can also cause the opposite effect in some people, leading to depigmented patches that resemble vitiligo. Folate deficiency produces similar changes.
Vitamin C deficiency causes a different kind of skin spots: tiny reddish or purple dots around hair follicles, caused by small hemorrhages beneath the skin. You might also notice corkscrew-shaped hairs surrounded by rough, bumpy plugs on the backs of your arms. These signs are uncommon in developed countries but can appear in people with very restricted diets.
How Dark Spots Are Treated
For hyperpigmentation from sun damage, hormones, or inflammation, the two most widely used topical treatments work in different ways. Hydroquinone suppresses melanin production directly, while retinoids (vitamin A derivatives) speed up skin cell turnover to push pigmented cells out faster. When compared head to head as supporting treatments alongside chemical peels for melasma, both showed similar results at 12 weeks. The difference showed up afterward: hydroquinone held results better over time, with only 28% of patients seeing their spots return, compared to 40% in the retinoid group.
Regardless of which treatment you use, sun protection is non-negotiable. UV exposure drives nearly every type of dark spot and will undo the progress of any treatment. Daily broad-spectrum sunscreen is the single most effective thing you can do to prevent new spots and keep existing ones from getting worse.
Spots That Need a Closer Look
Most skin spots are cosmetic concerns, not medical emergencies. But certain features warrant a dermatologist visit. The ABCDE rule, developed by the National Cancer Institute for screening melanoma, gives you a practical framework:
- Asymmetry: one half of the spot doesn’t match the other
- Border irregularity: ragged, notched, or blurred edges, with pigment spreading into surrounding skin
- Color variation: multiple shades of brown, black, tan, or unexpected colors like red, white, blue, or gray within a single spot
- Diameter: larger than 6 millimeters (roughly the size of a pencil eraser), or growing
- Evolving: any change in size, shape, color, or feel over weeks to months
A spot that bleeds, oozes, scabs over repeatedly without healing, or starts itching or burning also deserves professional evaluation. A dermatologist can examine it visually and perform a biopsy if anything looks uncertain. Catching a problem early makes a significant difference in outcomes, so err on the side of getting something checked rather than waiting.