\' are produced in the body. These occur naturally in your body. Periactin helps in these illnesses by stopping the unwanted effects of histamine and serotonin. Periactin is used for: Skin allergies with itchiness, swelling, or red skin, eczema or nettle rash Itchiness of chicken pox and reactions to insect bites and stings Sneezing, watery eyes and blocked or runny nose caused by an allergy (allergic rhinitis) Conjunctivis caused by an allergy - with red, watery, inflamed eyes Migraine and other similar headaches.