Detailed answer

Melasma and lichenoid dermatitis can both involve hyperpigmented skin lesions, leading to potential confusion in diagnosis. However, they have different underlying causes and distinct characteristics that can help differentiate between the two conditions.Melasma is a common acquired hyperpigmentation disorder that is primarily caused by hormonal factors, such as pregnancy or oral contraceptive use, but can also be influenced by sun exposure. It commonly appears as symmetric hyperpigmented macules or patches on the face, particularly on the cheeks, forehead, and upper lip. Histologically, melasma features increased melanin deposition and melanocyte activation in the epidermis.On the other hand, lichenoid dermatitis is an inflammatory skin condition characterized by an immune response to an antigen or trigger. The lesions of lichenoid dermatitis typically present as flat-topped papules or plaques with a lacy or reticular appearance. The distribution of lichenoid dermatitis is often more widespread than melasma, involving not only the face but also other areas of the body. Histologically, lichenoid dermatitis shows dense infiltration of lymphocytes along the dermoepidermal junction.While both melasma and lichenoid dermatitis can exhibit hyperpigmented skin lesions, a thorough evaluation that includes patient history, clinical examination, and skin biopsy can help differentiate between the two conditions. It is important to rule out other potential causes and consult with a dermatologist for an accurate diagnosis and appropriate treatment plan.