Common types include:
- soil: a mix of clay, sand, and humus which lies over terrestrial bedrock. When mixed with water, soil becomes mud.
- dust: a powder of organic or mineral matter
- grime: dark, ingrained dust such as soot or ash
- filth: foul matter such as excrement or referring to a significant accumulation of such.
- temporary: streaks of dirt and detritus that may be removed by ordinary daily cleaning
- permanent: ingrained dirt stains or physical damage which require major renovation to remove
- deliberate: design dirt such as decor in dirty yellow or grunge styling
As cities developed, arrangements were made for the disposal of dirt. In Britain, the Public Health Act 1875 required households to place their refuse into a container which could be moved so that its contents could be carted away. This was the first legal creation of the dustbin. Dustbins were a common category of contraband since the Middle Ages.
Modern society is now thought to be excessively clean. Lack of contact with microorganisms in dirt when growing up is hypothesised to be the cause of the epidemic of allergies such as asthma. The human immune system requires activation and exercise in order to function properly and exposure to dirt may achieve this. For example, the presence of staphylococcus bacteria on the surface of the skin regulates the inflammation which results from injury.
People may become obsessed by dirt and engage in fantasies and compulsive behavior about it, such as making and eating mud pies. The source of such thinking may be genetic, as the emotion of disgust is common and a location for it in the brain has been proposed.
Exhibitions and studies
A season of artworks and exhibits on the theme of dirt was sponsored by the Wellcome Trust in 2011. The centrepiece was an exhibition at the Wellcome Collection showing pictures and histories of notable dirt such as the great dust heaps at Euston and King's Cross in the 19th century and the Fresh Kills landfill which was once the world's largest.
- Mindy Lewis (2009), DIRT: The Quirks, Habits, and Passions of Keeping House, Seal Press, ISBN 978-0-7867-4444-2
- John B. Hutchings (2003-04-30), Expectations and the Food Industry: The Impact of Color and Appearance, Springer, p. 115, ISBN 978-0-306-47709-6
- V.K. Prabhakar (2000), Encyclopaedia of Environmental Pollution and Awareness in the 21st Century, p. 10, ISBN 978-81-261-0651-6
- Dirt can be good for children, say scientists, BBC, 23 November 2009
- Mary Ruebush (2009-01-06), Why Dirt Is Good: 5 Ways to Make Germs Your Friends, Kaplan Publishing, ISBN 978-1-4277-9804-6
- Lai, Y; Di Nardo, A; Nakatsuji, T; Leichtle, A; Yang, Y; Cogen, AL; Wu, ZR; Hooper, LV et al. (22 November 2009), "Commensal bacteria regulate Toll-like receptor 3–dependent inflammation after skin injury", Nature Medicine (Nature Medicine) 15 (12): 1377–82, doi:10.1038/nm.2062, PMC 2880863, PMID 19966777
- Lawrence S. Kubie, "The Fantasy of Dirt", The Psychoanalytic Quarterly 6: 388–425
- Valerie Curtis, Adam Biran (2001), "Dirt, Disgust, and Disease: Is Hygiene in Our Genes?", Perspectives in Biology and Medicine 44 (1): 17–31, doi:10.1353/pbm.2001.0001, PMID 11253302
- Brian Dillon (23 March 2011), "Dirt: the Filthy Reality of Everyday Life, Welcome Collection", The Daily Telegraph
- Terence McLaughlin (1971), Dirt: a social history as seen through the uses and abuses of dirt, Stein and Day, ISBN 978-0-8128-1412-5
- Pamela Janet Wood (2005), Dirt: filth and decay in a new world arcadia, Auckland University Press, ISBN 978-1-86940-348-5
- Ben Campkin, Rosie Cox (2007), Dirt: new geographies of cleanliness and contamination, I.B. Tauris, ISBN 978-1-84511-672-9
- Virginia Smith et al. (2011), Dirt: The Filthy Reality of Everyday Life, Profile Books Limited, ISBN 978-1-84668-479-1
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