1. Oral mucosa changes including stomatitis or lichenoid inflammation can give first evidence for such a contact allergy.

2. In Bullous LP, bullae are confined to lichenoid plaques, whereas in LPP, bullae are seen to arise independently from these plaques

3. Secondary syphilis and acrodermatitis chronica atrophicans regularly show a lichenoid infiltrate with interface dermatitis, whereas epidermal involvement is typically absent in erythema migrans, virus exanthema and bacillary angiomatosis.

4. In contrast to a decline of acute photo-allergic disorders there is an increase of persisting lichenoid light eruptions including severe types of pseudo-lymphomas (e.g., actinic reticuloid) in recent years.