Can i use carmex as a moisturiser on allergic dermatitis?

Yes but: I presume you meant atopic dermatitis or eczema. The major issue is a porous skin surface causing rapid water loss from the skin and making it easier for potential allergens to enter through it. Thus applying a good moisturizer within 3 minutes after bathing is important because this will help trap more water in your skin layer. Moisturizers i prefer include cerave, ulactin, or vanicream.