Seborrheic Keratosis

Overview

Seborrheic keratosis (also spelled seborrhoeic keratosis) is one of the most common benign skin growths in adults. These lesions are non-cancerous proliferations of keratinocytes that appear as waxy, well-demarcated, stuck-on growths on the skin surface. They are sometimes referred to as senile warts, barnacles, or basal cell papillomas, though they have no relation to viral warts or basal cell carcinoma.

Seborrheic keratoses are extremely common in individuals over the age of 50, although they can begin to appear from the third or fourth decade of life. They affect men and women equally and may occur as solitary lesions or in large numbers across the trunk, face, and extremities. The number of lesions tends to increase with age.

Causes and Risk Factors

The exact cause of seborrheic keratoses is not fully understood. They are not caused by sun exposure, although they tend to appear more frequently on sun-exposed areas. Research has identified somatic mutations in certain growth factor receptor genes, including FGFR3 and PIK3CA, in a proportion of seborrheic keratoses, suggesting a role for localised genetic changes in their development.

Known risk factors and associations include:

• Advancing age, with the prevalence increasing steadily after the age of 40.
• Genetic predisposition, as seborrheic keratoses frequently cluster in families.
• Hormonal influences, as new lesions may appear or existing ones may darken during pregnancy or oestrogen therapy.
• Skin friction, which may explain the tendency for some lesions to appear in skin fold areas.

Signs and Symptoms

Seborrheic keratoses present with characteristic features that typically allow clinical identification:

• Well-defined, round or oval lesions with a waxy, stuck-on appearance.
• Colour ranging from light tan to dark brown or black, though some may be flesh-coloured.
• A rough, warty, or velvety surface texture, sometimes with visible keratin-filled invaginations (horn cysts).
• Size ranging from a few millimetres to several centimetres in diameter.
• Most commonly found on the trunk, face, scalp, and extremities; lesions do not typically appear on the palms or soles.

Seborrheic keratoses are generally asymptomatic. However, they may become irritated by friction from clothing or jewellery, leading to itching, redness, or minor bleeding. Inflamed or traumatised lesions may be mistaken for other skin conditions, including skin cancer.

Diagnosis

Seborrheic keratoses are most often diagnosed by clinical examination and dermoscopy. Dermoscopic features include comedo-like openings, milia-like cysts, fissures and ridges, and a characteristic brain-like or cerebriform pattern. These features allow confident differentiation from melanocytic lesions and skin cancers in the majority of cases.

When the clinical or dermoscopic appearance is atypical, or when the lesion is heavily pigmented and difficult to distinguish from melanoma, a biopsy may be performed for histopathological confirmation. It is important to note that some melanomas may clinically mimic seborrheic keratoses, and any lesion with atypical features warrants careful evaluation by a dermatologist.

Treatment Options

Seborrheic keratoses are benign and do not require treatment unless they are symptomatic, cosmetically undesirable, or diagnostically uncertain. Several effective removal methods are available.

Cryotherapy: Liquid nitrogen is applied to the lesion to freeze and destroy the abnormal tissue. This is a commonly used, well-tolerated method suitable for flat to moderately raised lesions.

Curettage: The lesion is scraped off the skin surface using a curette, often under local anaesthesia. This method is effective for raised lesions and allows histological examination of the removed tissue.

Electrosurgery: High-frequency electrical current is used to ablate the lesion, often in combination with curettage. This approach provides effective removal with minimal bleeding.

Shave excision: The lesion is shaved off at the level of the surrounding skin using a blade or dermatome. This technique is suitable for raised or pedunculated lesions and allows histological examination.

When to Seek Medical Attention

A dermatologist should be consulted when a seborrheic keratosis changes rapidly in size, shape, or colour, when it bleeds without trauma, or when the diagnosis is uncertain. Any new or changing skin lesion that is heavily pigmented, irregular, or difficult to distinguish from melanoma warrants prompt dermatological assessment. While seborrheic keratoses are harmless, professional evaluation ensures that other conditions, including skin cancer, are not overlooked.