Exposure to sunlight can precipitate – a) Chloasmab) Discoid lupus erytyhematosusc) Dermatitis herpatiformisd) Lupus vulgaris

**Core Concept**
Exposure to sunlight can precipitate certain dermatological conditions due to its effects on the skin's immune response and DNA repair mechanisms. Ultraviolet (UV) radiation from sunlight can cause damage to skin cells, leading to an immune response and inflammation.

**Why the Correct Answer is Right**
The correct answer is **B. Discoid lupus erythematosus (DLE)**. DLE is a chronic autoimmune skin condition characterized by inflammation and scarring, often triggered by exposure to UV radiation from sunlight. This is because UV radiation can cause epidermal Langerhans cells to present self-antigens to T-cells, leading to an immune response against the skin. The pathogenesis of DLE involves the interaction between UV-induced DNA damage, immune cell activation, and the production of pro-inflammatory cytokines.

**Why Each Wrong Option is Incorrect**
**Option A:** Chloasma, also known as melasma, is a skin condition characterized by patches of discoloration, typically on the face. While it can be exacerbated by sun exposure, it is not typically precipitated by it.

**Option C:** Dermatitis herpetiformis is a skin condition characterized by blisters and intense itching. It is associated with celiac disease and is not directly precipitated by sun exposure.

**Option D:** Lupus vulgaris is a form of cutaneous tuberculosis, characterized by chronic inflammation and scarring. While it can be exacerbated by sun exposure, it is not typically precipitated by it.

**Clinical Pearl / High-Yield Fact**
Sun protection measures, such as sunscreen use and clothing, can help prevent the precipitation of DLE and other dermatological conditions triggered by UV radiation.

**Correct Answer:** B. Discoid lupus erythematosus