Acarodermatitis is a dermatitis caused by the bites of flour mites.


The disease is caused by the bites of pediculoides ventricosus, also known as flour mite, straw itch mite, or grain itch mite.

Figure 1 flour mite

Flour mites can be seen by the naked eye. They are yellowish brown, with an acicular proboscis on the head, two pairs of feet on the chest and abdomen respectively, and each foot has 5 segments. The unfertilized female mites are fusiform, about 0.2mm long, while the fertilized female mites are about 1mm long, and their abdomen enlarge into a ball. In the warm season, each female mite delivers about 200 - 300 mites, of which about 4% are male.

Signs and Symptoms

This disease mostly occurs in the warm, humid summer and autumn. Local persistent, severe pruritus occurs after being bitten, more severe at night. There are local edematous erythema, papules, papulovesicles, wheals, with petechiae on the center. Skin lesions occur initially on the contacting or exposed areas of the body, mostly on the neck and trunk, followed by the upper limbs, less common on the face and lower limbs. In severe cases, the skin lesions can be generalized, and there may be systemic symptoms, such as fever, headache, fatigue, asthma, and diarrhea. The skin lesions subside in about 1 week, and pruritus resolves, leaving pigmentation. There may be scratch marks, blood scabs, eczema, lymphadenopathy, and secondary infection as a result of scratches, and the condition can persist for many days. Patients are with increased white blood cells and eosinophils. Few patients may present with proteinuria, conjunctival hyperemia, and asthma.

Figure 2 acarodermatitis


If the condition occurs on the exposed areas contacting grains, and is under control quickly once patients stop contacting the contaminants, it can be diagnosed.


Children can be treated by topical dexamethasone cream and hydrocortisone cream, while adults can be treated with topical compound menthol tincture, antipruritic lotions, salicylic acid glycerin tincture, and compound triamcinolone acetonide ointment.