It seems that everything causes itching. Skin disorders, obviously, are a major culprit. Acne can itch. So can scars. Various bacterial, fungal, and viral infections also cause itching.
Some itches coincide with the seasons.
Hay fever, with itchiness of the eyes and nose, accompanies spring. Summer brings jellyfish stings, mosquito bites, poison-ivy rashes, prickly heat, and sunburn. Itching of the back, chin, or neck commonly precedes attacks of asthma, which often stems from allergies. Other causes of itching include aspirin, birth-control pills, the antimalarial drug chloroquine, morphine, penicillin, and rabies shots. Sometimes it's not the medication itself that causes the itch, but the dyes or preservatives in the product.