The actual warts can be a normal phenomenon, contact with allergic substances, secondary infections and so on. 1. Normal phenomenon: flat warts are usually found on the face, back of the hand and other parts of the skin, lesions for the high skin of the flat papules, rice grains to soybean size, if the local use of drugs coated, there may be a sudden number of lesions, dense, and consider the reaction of flat warts on the drug, so it can be manifested as a sudden increase in the number of lesions and especially itchy. 2. Contact with allergic substances: if the flat warts patients contact with allergic substances, such as pollen, dust mites, etc., and allergic to foreign drugs, the allergic substances will cause local skin stimulation, thus causing rashes, itching and other symptoms, which can be manifested as a sudden increase in the number of skin lesions and especially itchy. 3. secondary infection: for some of the flat warts patients, not pay attention to the skin care caused by secondary infection, bacteria, viruses and other pathogens can also cause skin stimulation, so the skin lesions suddenly increased and especially itchy phenomenon.