A 35-year-old farmer in rural Maharashtra develops acute contact dermatitis after handling poison ivy plants. Histopathology shows epidermal spongiosis with lymphocytic infiltration. Which of the following is the most common site of contact dermatitis in occupational settings in India?

Explanation

## Most Common Site of Contact Dermatitis in Occupational Settings **Key Point:** Hands and forearms are the most common sites of contact dermatitis in occupational settings because they are the primary sites of direct contact with irritants and allergens in the workplace. ### Pathophysiology of Contact Dermatitis (Type IV Hypersensitivity) **High-Yield:** Contact dermatitis is a delayed-type hypersensitivity reaction mediated by CD8+ T cells and Langerhans cells: 1. **Sensitization phase**: Hapten (small molecule) binds to skin proteins; Langerhans cells process and present antigen to T cells in regional lymph nodes 2. **Elicitation phase**: Re-exposure causes CD8+ T cell infiltration, leading to epidermal spongiosis and vesiculation 3. **Timeline**: Reaction develops 24–72 hours after exposure (delayed) ### Anatomical Distribution of Contact Dermatitis **Mnemonic: "HANDS First" — Hands, Arms, Neck, Digits, Scalp** | Site | Frequency | Occupational Examples | Reason | |---|---|---|---| | **Hands & forearms** | 70–80% | Farmers, mechanics, healthcare workers | Direct contact, high surface area, frequent exposure | | **Face & neck** | 10–15% | Cosmetics, airborne allergens | Secondary transfer, inhalation | | **Trunk** | 5–10% | Clothing contact, sweat-trapped allergens | Occlusion, friction | | **Lower extremities** | 2–5% | Footwear, plant contact | Less frequent exposure | ### Common Occupational Allergens in India **Clinical Pearl:** In rural and agricultural settings (common in India), the most frequent occupational contact allergens are: - **Plant-derived**: Poison ivy, poison oak, mango pollen, cashew shell oil, latex from rubber plants - **Chemical**: Pesticides, fertilizers, dyes, metals (nickel, chromium) - **Biological**: Latex, plant resins ### Histopathology of Contact Dermatitis **Key Point:** The histological finding of **epidermal spongiosis** (intercellular edema) with **lymphocytic infiltration** (predominantly CD8+ T cells) in the dermis is pathognomonic for contact dermatitis and confirms Type IV hypersensitivity. **Tip:** Hands and forearms show the highest concentration of Langerhans cells in the epidermis, making them particularly susceptible to sensitization and reaction.