Potassium alum, often shortened to alum, is a mineral salt that occurs naturally in the form of glassy, eight-sided white crystals. Due to its diverse range of functions, alum has been used by humans for thousands of years, and it remains popular today for purifying water, pickling foods, and serving as an ingredient in aftershave, tanning lotions and deodorants. Alum is also frequently used in cosmetics, including anti-aging products such as wrinkle creams.

Although alum naturally grows in the form of a crystal, it dissolves in water, liquefies with heat and can form an unstructured powder when processed at high temperatures, making it easy to mix with other ingredients in wrinkle creams. Though it can be mined from quarries, alum can be created synthetically by combining aluminum hydroxide with ammonium sulfate or potassium.

In wrinkle creams, alum acts as an astringent, causing a refreshing tingling sensation. Because alum tends to tighten the skin after application, it may temporarily reduce the appearance of wrinkles. This ingredient also has antimicrobial properties and can help wrinkle creams serve a dual function as bacteria-killing cleansers.

Alum may not be tolerated equally well by all people. According to a study published in the July 1999 issue of the journal "Cutis," some people experience skin irritation from using a deodorant containing alum. If you use exhibit dryness, itchiness, redness or other discomfort on your skin after applying alum-containing wrinkle cream, discontinue use and look for alternative products that are free of this ingredient.

The Cosmetic Ingredient Review, which is the main safety review board for substances used in cosmetics, has not evaluated the safety of alum for external use. However, the Food and Drug Administration has approved alum for use as a food bleaching agent, an ingredient in oral health items and an astringent in over-the-counter products.

According to the Skin Deep Cosmetic Safety Database, alum may be mutagenic, causing genetic disruptions in cells after exposure. Although mutagenic substances can potentially promote cancer, the amount of alum present in wrinkle creams may not be high enough to pose a threat. In addition, alum may be environmentally toxic by accumulating in the tissue of aquatic creatures. If you prefer earth-friendly cosmetic products, alum-containing wrinkle creams may not be suitable.