In emphasizing an ongoing procedure or set of habits for the purpose of maintenance and prevention, the concept of cleanliness differs from purity[disambiguation needed], which is a physical, moral, or ritual state of freedom from pollutants. Whereas purity is usually a quality of an individual or substance, cleanliness has a social dimension, or implies a system of interactions. "Cleanliness," observed Jacob Burckhardt, "is indispensable to our modern notion of social perfection." A household or workplace may be said to exhibit cleanliness, but not ordinarily purity; cleanliness also would be a characteristic of the people who maintain cleanness or prevent dirtying.
On a practical level, cleanliness is thus related to hygiene and disease prevention. Washing is one way of achieving physical cleanliness, usually with water and often some kind of soap or detergent. Procedures of cleanliness are of utmost importance in many forms of manufacturing.
Islam places great emphasis on cleanliness, in both its physical and spiritual aspects. On the physical side, Islam requires the Muslim to clean his body (wudu), his clothes, his house, and the whole community, and he is rewarded by Allah for doing so. Muhammad (SAW) said, "A Muslim is required to be pure morally and spiritually as well as physically." In the Qur'an, Allah commends those who are accustomed to cleanliness: "Allah loves those who turn to Him constantly and He loves those who keep themselves pure and clean." (2: 222). Muhammad once said "cleanliness is half of the faith".
Cleanliness is an important virtue, and all Hindus clean their homes particularly well in preparing to celebrate Diwali each year.
Main article: Hygiene
Since the germ theory of disease, cleanliness has come to mean an effort to remove germs and other hazardous materials. A reaction to an excessive desire for a germ-free environment began to occur around 1989, when David Strachan put forth the "hygiene hypothesis" in the British Medical Journal. In essence, this hypothesis holds that dirt plays a useful role in developing the immune system; the fewer germs people are exposed to in childhood, the more likely they are to get sick as adults. The valuation of cleanliness, therefore, has a social and cultural dimension beyond the requirements of hygiene for practical purposes.
In industry, certain processes such as those related to integrated circuit manufacturing, require conditions of exceptional cleanliness which are achieved by working in cleanrooms. 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. Cleanliness is also crucial for semiconductor manufacturing.
See also 
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|Look up cleanliness in Wiktionary, the free dictionary.|
- Aseptic technique
- Clean room
- Contamination control
- Green cleaning
- Lady Macbeth effect
- Environmental remediation
- Ritual purification
- Waste management
- Suellen Hoy, Chasing Dirt: The American Pursuit of Cleanliness (Oxford University Press, 1995), p. 3.
- Elizabeth Shove, Comfort, Cleanliness, and Convenience: The Social Organization of Normality (Berg, 2003), p. 80.
- Jacob Burckhardt, The Civilization of the Renaissance in Italy, as quoted by Douglas Blow, The Culture of Cleanliness in Renaissance Italy (Cornell University Press, 2006), p. 1.
- Kathleen M. Brown, Foul Bodies: Cleanliness in Early America (Yale University Press, 2009), p. 327; Iris Marion Young, "The Scaling of Bodies and the Politics of Identity," as excerpted in From Modernism to Postmodernism: An Anthology, edited by Lawrence E. Cahoone (Blackwell, 2003, 2nd ed.), p. 372; Nancy Cook, Gender, Identity, and Imperialism: Women Development Workers in Pakistan (Macmillan, 2007), p. 141.
- C. Y. Chang and Francis Kai, GaAs High Speed Devices: Physics, Technology, and Circuit Applications (John Wiley, 1994), p. 116.