What clinical features differentiate seborrhoeic keratosis from other benign skin lesions?

Seborrhoeic keratosis (SK) is clinically differentiated from other benign skin lesions by its characteristic appearance: SK lesions are typically well-demarcated, have a 'stuck-on' waxy or verrucous surface, and vary in colour from light tan to dark brown or black. They often present as raised plaques with a rough, papillomatous texture and may have small keratin-filled cysts visible on the surface, known as milia-like cysts. These features contrast with other benign lesions such as melanocytic naevi, which are usually smoother and more uniform in colour, or dermatofibromas, which are firm nodules with a central dimpling on lateral pressure. Additionally, SK lesions tend to occur in older adults and commonly appear on the trunk, face, and neck.

Importantly, SK lesions do not typically show signs of inflammation, ulceration, or rapid growth, which helps differentiate them from malignant or premalignant lesions. However, caution is advised as some melanomas can mimic SK clinically, especially when pigmented and verrucous, making dermoscopic evaluation or biopsy necessary in uncertain cases (Janowska et al., 2021).

UK clinical guidelines emphasize the importance of recognising these typical features to avoid unnecessary referrals but also recommend urgent referral if lesions show atypical features such as asymmetry, irregular borders, colour variegation, or rapid change, which may suggest malignancy rather than benign SK ¹.