Hello, Welcome to Just Answer and thanks for your question. Aspartamine taken in reasonable quantities has never been found to present any harm to anyone in scientific studies. Asthma itself is quite serious/dangerous and treating it is imperative. Singulair is a leukotriene inhibitor that prevents allergens from causing swelling in the lungs and airways. It is used in children as young as 2, often in conjunction with nebulizers. The puffiness in the face may be a result of the pulmicort which is a corticosteroid that may result in redistribution of body fat in different parts of the body, including the face. You should discuss your concerns with his treating doctors.