How can i protect from sunlight allergy ?

Cover up: You can't be truly "allergic" to the sun; your immune system can only make allergic antibodies to proteins. One of the syndromes to which you might be referring is polymorphic light eruption, which is a rash that occurs with the first significant sun exposure of the year, and lasts about a week. You have to wear loose-fitting clothing that covers the skin; sunscreens won't prevent this.