To provide an allergen-reducing fiber automatically reducing allergens sticking to the fiber, especially the allergens abundantly present in beddings, derived from the genus Dermatophagoides of the family Pyroglyphidae and causing allergic diseases at usually used humidity without carrying out an allergen-reducing treatment again and recovering allergen-reducing functions by simple operation.

The allergen-reducing fiber exhibits allergen-reducing effects in an atmosphere at ≤50 g/m3 absolute humidity.