Causes. While the cause of chronic idiopathic urticarial is unknown, the reaction may be caused by certain triggers, including pain medications, infection, insect bites or parasites, exposure to heat, cold or sunlight, stress, consumption of food or alcohol, or pressure on the skin.Common symptoms:hile the cause of chronic idiopathic urticarial is unknown, the reaction may be caused by certain triggers, including pain medications, infection, insect bites or parasites, exposure to heat, cold or sunlight, stress, consumption of food or alcohol, or pressure on the skin. Common symptoms: