Solar lentigo is a harmless patch of darkened skin resulting from local proliferation of melanocytes and accumulation of melanin within keratinocytes due to exposure to ultraviolet radiation. It is classically a flat, well-circumscribed patch. It can be round, oval or irregular in shape and may be slightly scaly.
Squamous cell carcinoma is a malignant tumour of epidermal keratinocytes that invades the dermis. It characteristically appears as slowly (weeks-months) enlarging scaly or crusted lumps. in sun-exposed areas. They may ulcerate and are usually tender or painful.
