Phenistil gel contains dimetindenum maleate, an active substance that belongs to the group of medicines called antihistamines. Phenistil gel is indicated for skin itching relief associated with skin reactions such as small skin rashes, hives, insect and marine animal bites, small sunburn and small surface burns, for adults and children from 1 month of age. You should see a doctor if it gets worse or if it does not improve after 7 days of treatment.