What causes scrotal nodular scabies?

Nodule formation in scrotal scabies is primarily associated with direct infestation by scabies mites, cutaneous immune-inflammatory responses, local skin characteristics, aggravated irritation from scratching, and incomplete treatment. It represents a typical manifestation of scabies at a specific stage of progression. If nodules continue to enlarge, severe itching occurs, or ulceration and secondary infection develop, prompt medical attention is recommended.

1. Direct mite infestation: Sarcoptes scabiei are transmitted through contact and invade the scrotal skin, burrowing into the epidermis to lay eggs. Their secretions, excretions, and the mites themselves irritate the skin, triggering localized inflammatory reactions that gradually lead to nodule formation.

2. Cutaneous immune-inflammatory response: Foreign body stimulation caused by the mites activates the body's immune system, leading to aggregation of inflammatory cells such as lymphocytes and eosinophils. These cells release inflammatory mediators, resulting in tissue hyperplasia and edema, which form firm nodules.

3. Local skin characteristics: The skin of the scrotum is thin, delicate, and rich in blood vessels. It remains in a warm, moist environment for prolonged periods—conditions favorable for mite survival and reproduction. Additionally, the skin barrier is relatively weak, making intense inflammatory reactions more likely and promoting nodule development.

4. Aggravation due to scratching: Intense itching leads to repeated scratching, which damages scrotal skin tissue, causes capillary dilation and tissue hyperplasia, and may push mites deeper into the skin. This exacerbates inflammation and results in further enlargement and hardening of the nodules.

5. Incomplete treatment: Failure to intervene early, insufficient medication dosage, or inadequate treatment duration may result in incomplete eradication of mites. Persistent mite activity continues to stimulate the skin, causing chronic inflammation and leading to refractory nodules that do not resolve spontaneously.

Treatment should follow medical guidance using targeted acaricidal agents and anti-inflammatory topical ointments, ensuring thorough application over the nodules and surrounding skin. Maintain cleanliness and dryness of the scrotal area, wear loose-fitting, breathable cotton clothing, avoid scratching and friction, and refrain from consuming spicy or irritating foods.