Mite dermatitis, also known as grain itch, grocer's itch, or straw itch, is an acute dermatitis caused by mite bites. It is a common skin disease in rural areas, often occurring among farmers who come into contact with grains, hence the name "grain itch."

bubble_chart Etiology

Disease causes: There are many types of mites, with an estimated 500,000 species worldwide. In China, the main mite causing grain itch is the Pyemotes ventricosus, also known as straw mite or mattress mite. They inhabit grains and primarily prey on insect larvae found in straw, cotton, and dry grass. The adult mites are earth-yellow and barely visible to the naked eye. Only female mites are harmful to humans, as they do not attach to the skin but temporarily bite it. Another type is the flour mite, which is found on foods such as flour, grains, ham, cheese, and dried fruits. Food handlers and warehouse workers may develop skin allergic reactions upon contact with the secretions or molted skins of flour mites.

bubble_chart Clinical Manifestations

This disease often occurs in warm and humid seasons such as summer and autumn. It manifests as round or oval-shaped, rice-sized to bean-sized red papules, papulovesicles, or edematous erythema on exposed or directly contacted areas of the skin. The center of the rash often shows needle-sized petechiae from insect bites, accompanied by intense cutaneous pruritus, especially at night. Scratching often leads to excoriations, blood crusts, or secondary infections. The rash is usually localized, but in severe cases, it can spread all over the body. Apart from cutaneous pruritus, there are generally no systemic symptoms, though some individuals may experience nausea, chest tightness, headache, lack of strength, fever, and other systemic symptoms. The course of the disease lasts about a week and may resolve on its own. Pyemotes dermatitis primarily presents as papules or blisters on exposed skin areas, which may develop secondary infections leading to pustules or eczema-like dermatitis.

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The main approach is symptomatic treatment, including antihistamines and topical application of calamine lotion, with antibiotics used for infections.

bubble_chart Prevention

The prevention of this disease mainly involves strengthening personal protection during the harvest season, such as fastening cuffs and trouser legs, and applying 5-7% naphthol ointment to the skin when necessary. Warehouses and storage areas should be well-ventilated, grains should be frequently sun-dried, and individuals should shower and change clothes after work.