I am constantly itchy at night, especially in my arms and legs. what can that be from?

Typically : Typically itching is due to an allergic reaction. The hard part is trying to figure out the cause. If it's at night then maybe it is something you are eating or drinking in the evening, a new blanket or sheets, possibly even a new detergent or soap you are using. Eliminating your exposure and foods one at a time will be time consuming yet may help reveal the cause. You could also visit your doctor for an evaluation to rule out other causes and possibly allergy testing if deemed necessary. Good luck.

Nocturnal itching: Causes of itching without skin rash includes excessively dry skin, diabetes, liver or kidney disease and some types of allergic reactions, very thick blood(polycythemia), lymphoma, some infections. See your physician for evaluation and testing.