Skin is the body’s largest organ, and it often reflects what is happening internally. Changes in pigmentation — including dark marks, patches, or spots — are common and usually harmless. Sun exposure, aging, hormonal shifts, and minor injuries can all cause darker areas on the skin.

However, in some cases, persistent or unusual dark marks may signal underlying health conditions that require medical evaluation.

It is important to emphasize that most dark spots are benign. The key factors that determine concern are changes in appearance, rapid growth, irregular borders, accompanying symptoms, or persistence without clear cause.

Here are five types of dark skin changes that should not be ignored.

1. A Dark Mole That Changes Shape, Size, or Color

Moles are common. Most people have between 10 and 40 moles on their body. However, certain changes may indicate melanoma, a serious form of skin cancer.

Doctors often recommend using the ABCDE rule to evaluate moles:

• A – Asymmetry (one half does not match the other)

• B – Border irregularity (uneven, blurred, or jagged edges)

• C – Color variation (multiple shades of brown, black, red, or blue)

• D – Diameter (larger than 6 mm, though melanomas can be smaller)

• E – Evolving (any change over time)

A mole that darkens rapidly, bleeds, itches persistently, or changes in texture should be examined by a dermatologist.

Early detection of melanoma significantly improves treatment outcomes.

2. Dark Patches on the Neck or Underarms (Acanthosis Nigricans)

Velvety, thickened dark patches — especially on the neck, armpits, groin, or knuckles — may indicate acanthosis nigricans.

This condition is often associated with:

• Insulin resistance

• Type 2 diabetes

• Obesity

• Polycystic ovary syndrome (PCOS)

In rare cases, sudden and widespread acanthosis nigricans in adults may be associated with internal malignancy, particularly gastrointestinal cancers.

When these patches appear without clear explanation or worsen rapidly, blood sugar testing and medical evaluation are advised.

3. Dark Streaks Under the Nails

A brown or black line under the nail can have several causes, including trauma. However, a condition known as subungual melanoma can appear as a dark streak beneath the nail plate.

Warning signs include:

• A dark band that widens over time

• Pigment spreading to surrounding skin

• No history of injury

• Nail splitting or bleeding

Because nail melanoma is often mistaken for bruising, diagnosis may be delayed. Persistent discoloration under the nail should be assessed by a healthcare professional.

4. Sudden Appearance of Multiple Dark Spots

The rapid development of numerous dark, wart-like growths — especially in older adults — may indicate a phenomenon known as the Leser-Trélat sign.

This sign involves the sudden eruption of multiple seborrheic keratoses and may, in rare cases, be associated with internal malignancies.

While most seborrheic keratoses are harmless, a sudden increase in number or size warrants medical attention.

Additionally, dark spots that appear alongside unexplained weight loss, fatigue, or gastrointestinal symptoms should not be ignored.

5. Generalized Darkening of the Skin (Hyperpigmentation)

Widespread darkening of skin folds, scars, or mucous membranes may signal hormonal disorders.

One notable condition is Addison’s disease, a disorder of the adrenal glands. When cortisol levels are insufficient, the body produces excess ACTH, which can stimulate melanin production.

Signs may include:

• Darkening of elbows, knees, and knuckles

• Dark patches inside the mouth

• Fatigue

• Low blood pressure

• Unexplained weight loss

Although rare, adrenal disorders require prompt medical management.

When to Seek Medical Attention

Not every dark mark indicates serious illness. However, medical evaluation is recommended if:

• A spot changes rapidly

• Borders are irregular or uneven

• There is bleeding or persistent itching

• New marks appear suddenly and multiply

• Darkening occurs with other unexplained symptoms

Dermatologists can perform dermoscopic examination or biopsy when necessary.

Why Monitoring Skin Changes Matters

The skin often provides early clues about:

• Hormonal imbalances

• Metabolic disorders

• Immune dysfunction

• Circulatory issues

• Malignancies

Regular self-examination can help identify changes early.

Doctors recommend:

• Checking skin monthly

• Using mirrors to inspect hard-to-see areas

• Photographing suspicious spots for comparison

• Scheduling annual skin exams if at higher risk

Final Thoughts

Dark marks on the skin are common and usually harmless. However, changes in size, color, shape, or number - especially when accompanied by systemic symptoms - deserve attention.

Early medical evaluation does not mean something serious is present. It simply ensures that, if there is an underlying condition, it can be addressed promptly.

Listening to changes in the body - including those visible on the skin is an important step in maintaining long-term health.