Alum is a compound that contains aluminum. In cosmetics, “alum” usually refers to potassium alum, which has astringent and antibacterial properties.

An astringent causes tissues to contract, making them shrink or tighten. People sometimes use astringents to reduce the appearance of pores on the skin.

Alum has a range of topical uses, including as an antiperspirant deodorant. It also features as an ingredient in certain products, such as styptic pencils, which help seal cuts from shaving.

However, the Environmental Working Group (EWG) notes that there are concerns that potassium alum may not be safe for long-term use. Some studies have found a relationship between deodorants that contain potassium alum and rates of breast cancer, but others do not agree with this finding.

In this article, we will look more closely at what alum is, its properties, uses, and risks.

A woman rolling alum crystal deodorant on the skin under one arm.Share on Pinterest
Asya Molochkova/Stocksy

Alum is a term that can refer to several aluminum compounds. In cosmetics, it usually refers to potassium alum, a type of mineral salt.

Other types of alum include:

  • soda alum
  • ammonium alum
  • chrome or chromium alum

Potassium alum has several properties that companies utilize in personal care products.

Firstly, it is an astringent, meaning it causes the skin to contract or shrink. Astringents can temporarily reduce the size of pores and tighten the skin.

Alum is also bacteriostatic, which means it prevents bacteria from growing, making it useful as a preservative. It can reduce bacterial growth in personal care products and extend their shelf life.

In the production of vaccines, alum is also a common adjuvant, which means it enhances the immune system’s response to the shot. However, scientists are not sure how it does this.

Below are some of the topical uses for alum.

Shaving

Alum blocks make for popular shaving products because they prevent bacterial growth and reduce inflammation. This may help reduce the risk of a shaving rash or infection.

Alum is also an ingredient in styptic pencils, another shaving product that manufacturers make by fusing potassium alum with potassium nitrate. Styptic pencils are anti-hemorrhagic agents that treat shaving cuts by aiding clotting and quickly sealing the wound.

Antiperspirant deodorant

Alum is a popular ingredient in antiperspirants for its ability to reduce sweating. It is available in both standard deodorants and as a block that people get wet and then rub directly under the arms. Some companies refer to these products as “crystal deodorants.”

These deodorants may work by shrinking sweat ducts and reducing bacteria that cause body odor.

Acne

Because it is an astringent and inhibits bacteria, some people use alum to reduce oily skin and acne. However, while no research indicates whether it is an effective treatment for either of these, anecdotal reports state that it helps.

Alum may also appear on the ingredients list of skin whitening products, but there is no evidence it lightens the skin.

People have used alum medicinally for a long time. However, it is unclear if it has any long-term benefits for skin health, as there are no scientific studies on this topic. Much of what people know about alum’s properties come from anecdotal evidence or observation.

Scientists do know that alum inhibits the growth of several common strains of bacteria, including Staphylococcus and Streptobacillus. A 2014 laboratory study proved this by taking swabs from the armpits of five male participants, growing the bacteria in agar plates, and exposing them to alum.

However, this study only showed how well alum works in laboratory conditions on agar plates rather than on human skin.

Alum may carry some potential risks, which include the below.

Poisoning

If a person gets alum or styptic pencil in their eyes, it can cause irritation. In some cases, it may cause long lasting damage.

If alum gets in the eyes, a person should remove any glasses or contact lenses immediately and rinse the eye continuously with room temperature water for 15–20 minutes.

Alum products can also cause mild poisoning if an individual ingests them, which may lead to nausea, vomiting, or an upset stomach. However, these symptoms should resolve quickly, and eating or drinking may reduce their effects.

If someone swallows a larger amount of alum or part of a styptic pencil, or if they have impaired kidney function, they should contact Poison Control for help.

Breast cancer

The EWG notes that some studies have found a relationship between antiperspirants containing aluminum and higher incidences of breast cancer. However, some older studies on this topic have not yielded the same results.

A 2017 study of over 400 females found that the frequent use of aluminum-containing antiperspirants had links to the presence of aluminum in breast tissue.

Participants with breast cancer had higher concentrations of aluminum in their breast tissue compared with the healthy controls without the disease, suggesting this may be a risk factor for breast cancer development.

However, more research is necessary to prove if aluminum in breast tissue can raise the risk of breast cancer.

Alzheimer’s disease

An older 2008 review of 34 studies found an association between aluminum and the neurological processes responsible for Alzheimer’s disease. However, the review did not look at the use of alum specifically. Instead, it examined the risk from aluminum exposure of any kind, including topical, oral, and environmental.

Therefore, more specific studies on topical alum use are necessary to see if there are correlations with Alzheimer’s disease.

Environmental toxin

Environmental scientists believe alum may be toxic to the environment, adding that they suspect it may also be bioaccumulative. This means the substance accumulates in habitats or the bodies of animals, rather than breaking down. More research is necessary to understand if this is the case and what the effects are.

If a person chooses to use alum, there are several ways to do this:

  • Alum block: After shaving, rinse the skin with cold water, then wet or soak the alum block in cold water. Run the block over the skin and allow the residue to remain in place for a few seconds before rinsing. Then apply moisturizer or aftershave.
  • Styptic pencil: To treat small cuts, wash the hands and then wet the tip of the styptic pencil. Press the tip directly onto the cut and hold for a few seconds or until the bleeding stops.
  • Styptic powder: Alternatively, apply a pinch of styptic powder and press against the cut until the bleeding stops.

Using alum on the skin can sometimes cause side effects. These may include:

  • tingling
  • tightness
  • dryness
  • itchiness

It may also be possible for people to have an alum allergy, although a lack of strong evidence makes this difficult to determine. An older 2008 study of deodorant ingredients found that while many contained aluminum, many also contained other common allergens, such as:

  • fragrance
  • propylene glycol
  • essential oils

If any personal care product causes adverse effects, a person should wash it off and stop using it.

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

  • hives
  • swelling of the face or mouth
  • wheezing
  • fast, shallow breathing
  • a fast heart rate
  • clammy skin
  • anxiety or confusion
  • dizziness
  • vomiting
  • blue or white lips
  • fainting or loss of consciousness

If someone has these symptoms:

  1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
  2. Dial 911 or the number of the nearest emergency department.
  3. Lay the person down from a standing position. If they have vomited, turn them onto their side.
  4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one.

Alum is an aluminum compound with many uses. For example, people can use alum blocks as antiperspirant deodorants to reduce post-shave irritation or stop bleeding from small cuts.

Alum is an astringent and bacteriostatic agent, meaning it inhibits bacterial growth. However, some studies suggest that aluminum-containing deodorants may increase the risk of breast cancer.