question: Why is the deodorant *can* always cold to the touch?
comment: The deodorant is propelled out of the can by a substance that is aptly named the propellant. That propellant is compressed inside the can (often into a liquid), and as deodorant is sprayed the propellant rapidly evaporates and expands to propel the substance it is spraying. This expansion and evaporation require heat to take place, heat which the propellant extracts from the air and the can around it. Therefore the can gets cold, as does the air immediately surrounding it. This is exactly the same process by which air conditioners or refrigerators work, although the mechanism is quite different.
passages: Underarm hair wicks the moisture away from the skin and aids in keeping the skin dry enough to prevent or diminish bacterial colonization. The hair is less susceptible to bacterial growth and therefore reduces bacterial odor. The apocrine sweat glands are inactive until puberty, which is why body odor often only becomes noticeable at that time.
  
  Deodorant products work in one of two ways - by preventing sweat from occurring, or by allowing it to occur but preventing bacterial activity that decomposes sweat on the skin.
  
  Section::::History.
  
  Section::::History.:Early deodorants.
   Human perspiration of all types is largely odorless until its organic components are fermented by bacteria that thrive in hot, humid environments. The human underarm is among the most consistently warm areas on the surface of the human body, and sweat glands readily provide moisture containing a proportion of organic matter, which when excreted, has a vital cooling effect. When adult armpits are washed with alkaline pH soap, the skin loses its protective acid mantle (pH 4.5 - 6), raising the skin pH and disrupting the skin barrier. Many bacteria are adapted to the slightly alkali environment within the human body, so they can thrive within this elevated pH environment. this makes the skin more than usually susceptible to bacterial colonization. Bacteria on the skin feed on the waste proteins and fatty acids in the sweat from the apocrine glands and on dead skin and hair cells, releasing trans-3-methyl-2-hexenoic acid in their waste, which is the primary cause of body odor. 
   Section::::Classification.
  
  Section::::Classification.:Deodorant.
   The FDA has "acknowledge[d] that small amounts of aluminium can be absorbed from the gastrointestinal tract and through the skin", leading to a warning "that people with kidney disease may not be aware that the daily use of antiperspirant drug products containing aluminium may put them at a higher risk because of exposure to aluminium in the product." The agency warns people with kidney dysfunction to consult a doctor before using antiperspirants containing aluminum.
  
  Section::::Health effects.:Aerosol burns and frostbite.
   In 2007, Procter & Gamble introduced Secret Clinical Strength, the first product from Secret promising clinical strength wetness protection without a prescription.
  
  In 2008, Secret’s scientists developed Secret Flawless, a wetness improvement over the formula featured in their Platinum line. Secret Flawless features proprietary scent renewing technology and movement-activated protection. 
  
  In 2009, Scent Expressions was launched and featured 11 unique scents. This line of Secret products was designed to meet growing consumer interest in scent-based deodorants. Also launched was the brand’s first waterproof deodorant, Secret Clinical Strength Waterproof.
   Section::::Inert atmosphere work.
   The US Food and Drug Administration, in a 2003 paper discussing deodorant safety, concluded that "despite many investigators looking at this issue, the agency does not find data from topical and inhalation chronic exposure animal and human studies submitted to date sufficient to change the monograph status of aluminum containing antiperspirants", therefore allowing their use and stating they will keep monitoring the scientific literature. Members of the Scientific Committee on Consumer Safety (SCCS) of the European Commission concluded similarly in 2015, that "due to the lack of adequate data on dermal penetration to estimate the internal dose of aluminium following cosmetic uses, risk assessment cannot be performed."
   Early product innovations were driven by the principle that men and women may have different needs when it comes to odor protection, but women should never have to compromise on efficacy. The slogan “Strong Enough for a Man, Made for a Woman” was developed in the early 1970s and grew to become one of Secret’s most famous advertising tag lines. (Reference: P&G Corporate Archives)
  
  The 1980s
   During the 1980s, Secret adapted the solid antiperspirant/deodorant from a round stick to a wide stick in order to better fit under a woman’s arm. Secret also introduced three new scents: Powder Fresh, Spring Breeze and Sporty Clean, to meet growing consumer demand for a variety of scents. By the end of the 1980s, Secret was the leading women’s deodorant brand in dollar sales.
  
  The 1990s
   In 2010, Secret was one of several brands featured in Procter & Gamble’s sponsorship of the 2010 Winter Olympics. The “Thank you Mom” campaign featured athletes and their mothers. Secret worked with Tanith Belbin, Allison Baver and Allison Baver’s mother. Secret launched an online campaign, “Let Her Jump,” which promoted making women’s ski jumping an official Olympic sport.
   The 7.4-volt battery is the most common type of heated clothing battery system, and may be rechargeable. The most popular items sold have traditionally been heated gloves and jackets.
   Section::::Health effects.:Aluminum.:Myths and claims related to aluminium compounds in deodorants.
  
  Common myths and marketing claims for aluminium in deodorants (including aluminum in alum products) include claims:
  
  BULLET::::- That aluminium in deodorants applied to the skin is a risk factor for some cancers (notably breast cancer) and some forms of dementia.
  
  BULLET::::- That aluminium in antiperspirants can enter the body (possibly through shaving cuts).
  
  BULLET::::- That aluminium in alum "natural deodorant" products is "safer" because it is "too large" to enter the body.
   Secret (deodorant brand)
  
  Secret is an antiperspirant/deodorant for women manufactured by Procter & Gamble. It is sold in the United States, Canada, and Mexico. Secret was launched as the first female deodorant in 1956, after more than 10 years of research that began in 1945. Secret is the only female brand antiperspirant/deodorant in Procter & Gamble’s portfolio of products, which includes male brands Gillette and Old Spice.
   In the United States, deodorants are classified and regulated as cosmetics by the U.S. Food and Drug Administration (FDA) and are designed to eliminate odor. Deodorants are often alcohol based. Alcohol initially stimulates sweating but may also temporarily kill bacteria. Other active ingredients in deodorants include sodium stearate, sodium chloride, and stearyl alcohol. Deodorants can be formulated with other, more persistent antimicrobials such as triclosan that slow bacterial growth or with metal chelant compounds such as EDTA. Deodorants may contain perfume fragrances or natural essential oils intended to mask the odor of perspiration. In the past, deodorants included chemicals such as zinc oxide, acids, ammonium chloride, sodium bicarbonate, and formaldehyde, but some of these ingredients were messy, irritating to the skin, or even carcinogenic.
   BULLET::::- "Aluminum in antiperspirants can enter the body (possibly through cuts) and cause breast cancer:" There is no current evidence to support this claim, nor any convincing evidence that it is true. A fact often cited to back up this claim is that more breast cancers occur in the part of the breast near the armpits, however breast tissue is not evenly spread out, and the part of the breast near the armpit (the Tail of Spence) simply contains much more breast tissue than the other quadrants, making it much more likely that any cancer would occur in that location. See above for current scientific knowledge regarding aluminum in deodorants.
   The myth that breast cancer is believed to be linked with deodorant use has been widely circulated and appears to originate from a spam email sent in 1999; however, there is no evidence to support the existence of such a link. The myth circulates in two forms:
   There is a popular myth that deodorant use is linked to breast cancer, but research has shown no such link exists.
  
  Section::::Overview.
   Section::::Conception.:Packaging and scent.
   Of note, the parts of the body which are commonly shaved and also commonly treated with deodorants, such as the armpits, contain substantial deposits of subcutaneous fat. Shaving cuts would be extremely unlikely to penetrate sufficiently beyond the very outer layers of the skin, for much if any product to enter the bloodstream.
  
  Section::::Health effects.:Aluminum.:Alzheimer's disease.
   Procter & Gamble began research on the product that would be Secret’s first in 1945. In 1956, Secret was introduced as a cream that was applied with fingers to the underarm area for underarm odor control. It was the first antiperspirant/deodorant product made for, and marketed to, women. In 1958, Secret introduced a roll-on product, with a spray following in 1964. The solid round stick version was launched in 1978.
   The scent's Energizing Shower Gel was released exclusively in Europe, in one size—
  
  BULLET::::- 200ml / 6.7 oz
   In the United States, the Food and Drug Administration classifies and regulates most deodorants as cosmetics but classifies antiperspirants as over-the-counter drugs.
  
  The first commercial deodorant, Mum, was introduced and patented in the late nineteenth century by an inventor in Philadelphia, Pennsylvania, Edna Murphey. The product was briefly withdrawn from the market in the US. The modern formulation of the antiperspirant was patented by Jules Montenier on January 28, 1941. This formulation was first found in "Stopette" deodorant spray, which "Time" magazine called "the best-selling deodorant of the early 1950s".
   Section::::Promotion.:Commercial.
   Aerosol burn
  
  An aerosol burn is an injury to the skin caused by the pressurized gas within an aerosol spray cooling quickly, with the sudden drop in temperature sufficient to cause frostbite to the applied area. Medical studies have noted an increase of this practice, known as "frosting", in pediatric and teenage patients.
  
  Adiabatic expansion causes the gas (with a low boiling temperature) to rapidly cool on exit from the aerosol applier. According to controlled laboratory experiments, the gas from a typical deodorant spray can reduce skin temperature by up to sixty degrees Celsius.
   In a 2010 article published in the "Daily Mail" Laura Stott described being allowed to wear a prototype spray-on shirt, and being pleasantly surprised that it did not tear, or rip, when she hung her large handbag from her shoulder. She said she was able to take off the shirt as easily as any t-shirt, and that it retained its shape on subsequent wearings.
  