However, dirt may play a useful role in our immune systems. This shift in thinking can be traced back to 1989, when David Strachan put forth the "hygiene hypothesis" in the British Medicine Journal. Strachan looked at the records of 17,000 British children and found that the greater number of older siblings they had, the less likely they were to come down with hay fever—a disease which, despite its name, is far more common in the city than the country. Strachan wondered if the older children were bringing home more viral infections to their younger siblings, priming their immune systems so they could better tolerate pollen. The "hygiene hypothesis" has now been linked with asthma, allergies, intestinal diseases including Crohn's disease Fact: date=February 2007, childhood leukaemia Fact: date=February 2007 and atopic dermatitis and the list is growing.

Cleanliness is essential to successful electroplating, since molecular layers of oil can prevent adhesion of the coating. The industry has developed specialized techniques for parts cleaning, as well as tests for cleanliness. The most commonly used tests rely on the wetting behaviour of a clean hydrophillic metal surface.

Cleanliness is also important to vacuum systems to reduce outgassing.

See also

• Antiseptic
• Aseptic technique

  Category:Cleaning tools

  Category:Cleaning products

  References

  • Boy Scouts. 2007. "Boy Scout's Oath, Law, Motto, and Slogan." Retrieved May 10, 2007, http://www.scouting.org/Media/FactSheets/02-503a.aspx