Alum is a type of astringent, which is a substance that causes the contraction of body tissues. It is commonly used in medicine and cosmetics to reduce inflammation and irritation. ALUM is a naturally occurring mineral salt composed of aluminum sulfate and potassium sulfate. It has been used for centuries as an antiseptic, astringent, and styptic. It is also used in pickling and preserving foods, and as a mordant in dyeing fabrics.