## Distribution of Scabies Lesions **Key Point:** Scabies has a characteristic distribution pattern that spares the scalp and face in immunocompetent adults, though these sites may be involved in infants, elderly, and immunocompromised patients. ### Classic Sites of Involvement (in order of frequency) | Site | Frequency | Reason | | --- | --- | --- | | Interdigital spaces (fingers) | Most common | High moisture, thin stratum corneum, frequent contact | | Flexural wrists | Very common | Warm, moist microenvironment | | Genitalia, lower abdomen | Very common | Thin skin, warm, moist | | Buttocks, axillae | Common | Intertriginous areas | | Breasts (women) | Common | Inframammary fold | | Elbows | Moderately common | Flexural surface | | Ankles, feet | Moderately common | Similar to wrists | | **Scalp, face** | **Rarely affected** | Thick stratum corneum, frequent washing, less suitable for mite survival | **High-Yield:** Scalp and facial involvement in scabies should raise suspicion for: - Infants and young children (< 2 years) - Elderly patients - Immunocompromised individuals (HIV/AIDS) - Crusted (Norwegian) scabies **Mnemonic:** **FIFE** — Fingers, Interdigital spaces, Flexural wrists, External genitalia (common sites to check first) ### Why Scalp/Face Are Spared 1. **Thick stratum corneum** on scalp resists mite penetration 2. **Frequent washing** of face and scalp reduces mite survival 3. **Sebaceous gland secretions** may be hostile to mites 4. **Lower humidity** compared to intertriginous areas **Clinical Pearl:** If you see scabies on the scalp and face in an adult, always investigate for immunosuppression (HIV, malignancy, immunosuppressive therapy) or consider crusted scabies. 
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