Allergies: Allergic reactions to certain substances, which are triggered when the individual comes in contact with the allergens, are known to cause skin itch in some people. These allergens include certain foods, pollen, plants like poison ivy and poison oak, lacquer, in some people even cosmetics and hair dye, chemicals, wool, etc. In this case, the itching sensation may either last for a few hours or even go on for a few days.