Hello and welcome to healthcaremagic Extreme dry skin of arms and legs along with keratosis pilaris is a feature of atopic dermatitis/atopy OR Icthyosos Vulgaris. In atopics the skin has low water retention capacity as a result they have dry skin, rough skin. Icthyosis vulgaris is due to defective fillagrin gene/mutations thereby leading to a defective epidermal barrier and increased transepidermal water loss. This is not due to deficiency of essential fatty acids. Moisturizers specially those that contain hygroscopic ingredients (which attract water from the atmosphere) like glycerin, hyaluronic acid etc and exfoliating agents like glycolic acid, ammonium lactate etc are specially useful for dry skin conditions seen in atopics and icthyosis. The exfoliating action of glycolic acid and ammonium lactate is also helpful in treatment of keratosis pilaris. Hope this helps Regards