Stinging nettle
The stinging nettle (Urtica dioica) is a herbaceous flowering plant, native to Europe, Asia, northern Africa, and North America, and is the best known member of the nettle genus Urtica. This species have spiny hairs, or stinging trichomes, whose tips come off when touched, transforming the hair into a needle that will inject a cocktail of poisons: acetylcholine, histamine, 5-HT and possibly  formic acid. This mix of poisons cause a sting or paresthesia from which the species derives its common name, as well as the colloquial name "7 minute itch".
The taxonomy of stinging nettles in the genus Urtica has been confused, and older sources are likely to use a variety of systematic names for these plants. Formerly, more species were recognised than are now accepted. However, there are at least five clear subspecies, some formerly classified as separate species:
- U. dioica subsp. dioica (European stinging nettle). Europe, Asia, northern Africa.
- U. dioica subsp. afghanica. Southwestern and central Asia. (Gazaneh in Iran)
- U. dioica subsp. gansuensis. Eastern Asia (China).
- U. dioica subsp. gracilis (Ait.) Selander (American stinging nettle). North America.
- U. dioica subsp. holosericea (Nutt.) Thorne (hairy nettle). North America.
Other species names formerly accepted as distinct by some authors but now regarded as synonyms of U. dioica include U. breweri, U. californica, U. cardiophylla, U. lyalli, U. major, U. procera, U. serra, U. strigosissima, U. trachycarpa, and U. viridis. Other vernacular names include tall nettle, slender nettle, California nettle, jaggy nettle, burning weed, and bull nettle (a name shared by Cnidoscolus texanus and Solanum carolinense).
Stinging nettles are a herbaceous perennial, growing to 1-2 m tall in the summer and dying down to the ground in winter. It has very distinctively yellow, widely spreading roots. The soft green leaves are 3-15 cm long, with a strongly serrated margin, a cordate base and an acuminate tip.
Stinging nettles are abundant in northern Europe and much of Asia, usually found in the countryside. It is less gregarious in southern Europe and north Africa, where it is restricted by its need for moist soil. In North America it is widely distributed in Canada and the United States, where it is found in every province and state except for Hawaii and also can be found in northernmost Mexico. In North America the stinging nettle is far less common than in northern Europe. The European subspecies has been introduced into North America as well as South America.
In the UK stinging nettles have a strong association with human habitation and buildings. The presence of nettles may indicate that a building has been long abandoned. Human and animal waste may be responsible for elevated levels of phosphate and nitrogen in the soil, providing an ideal environment for stinging nettles. This seems particularly evident in Scotland where the sites of crofts razed to the ground during the Highland Clearances can still be identified.

# Medicinal uses
Stinging nettle has many uses. It is used by many different cultures for a wide variety of purposes in herbal medicine and is known to have been used as far back as ancient Greece.
Nettle leaf is an herb that has a long tradition of use as an adjuvant remedy in the treatment of arthritis in Germany. Nettle leaf extract contains active compounds that reduce TNF-a and other inflammatory cytokines. (31. Teucher T, et al. . Arzneimittelforschung 1996 Sep;46(9):906-10.
32. Obertreis B, et al. Ex-vivo in-vitro inhibition of lipopolysaccharide stimulated tumor necrosis factor-alpha and interleukin-1 beta secretion in human whole blood by extractum urticae dioicae foliorum. Arzneimittelforschung 1996 Apr;46(4):389-94. Published erratum appears in Arzneimittelforschung 1996 Sep;46(9):936.)
Not only does nettle leaf lower TNF-a levels, but it has been demonstrated that it does so by potently inhibiting the genetic transcription factor that activates TNF-a and IL-1B in the synovial tissue that lines the joint.(33) (33. Riehemann K, et al. Plant extracts from stinging nettle (Urtica dioica), an antirheumatic remedy, inhibit the proinflammatory transcription factor NF-kappaB. FEBS Lett 1999 Jan 8;442(1):89-94.)
A study on healthy volunteers demonstrated the anti-inflammatory potential of nettle.(32) In this study, nettle extract significantly reduced TNF-a and IL-1B concentration in response to stimulation by these pro-inflammatory cytokines.
Another study conducted on forty patients suffering from acute arthritis compared the effects of 200 mg of an anti-inflammatory drug (diclofenac) with only 50 mg of the same drug in combination with stewed nettle leaf.(34) (34. Chrubasik S, et al. Evidence for antirheumatic effectiveness of Herba Urticae in acute arthritis: a pilot study. Phytomedicine 1997 4:105-108.
Total joint scores improved significantly in both groups by approximately 70%. The addition of nettle extract made possible a 75% dose reduction of the toxic drug, while still retaining the same anti-inflammatory benefits with reduced side effects. This study implies that people taking nettle extract could possibly reduce their dose of a COX-2 inhibiting drug, while at the same time protecting against the recently discovered potential adverse of effects of COX-2 inhibitors, i.e. elevated TNF-a and IL-1B.
Please note that an extract from the nettle root (Urtica dioica) is used to alleviate symptoms of benign prostate enlargement. Nettle leaf extract, on the other hand, is what has been shown to reduce the pro-inflammatory cytokines TNF-a and IL-B1.
Cooking, crushing or chopping disables the stinging hairs. Stinging nettle leaves are high in nutrients, and the leaves can be mixed with other ingredients to create a soup rich in calcium and iron. Nettle soup is a good source of nutrients for people who lacked meat or fruit in their diets. The young leaves are edible and make a very good pot-herb. The leaves are also dried and may be then be used to make a tisane, as can also be done with the nettle's flowers. Because stinging nettle usually grows at nitrogen-rich places, it often contains high concentrations of nitrate which can be converted in the digestive tract to carcinogenic nitrosamines and should therefore not be used for baby food.
Nettle stems contain a bast fibre which has been traditionally used for the same purposes as linen, and is produced by a similar retting process.

# Anti-itch treatment
If stung by a nettle effective anti-itch drugs are available, usually in the form of creams containing antihistaminics or hydrocortisone. Many folk remedies exist for treating the itching, but most of them are ineffective or provide only a short relief simply by mechanical stimulation similar to scratching or by cooling:
- Juice from the crushed leaf of dock (Rumex spp.), which commonly grows in association with nettles, rubbed into the area
- Juice from both species of Jewelweed (Impatiens capensis and Impatiens pallida), rubbed into the area
- Rubbing the underside of a fern leaf (which contains its spore pods or sori) on the afflicted area.
- Immediately rubbing mud on the affected area and allowing it to dry before brushing it clean.
- Quickly washing the affected area.
- Applying ice can help relieve itchiness.
- Moistening the irritated area with saliva.
- Smearing the infected area with a paste of Baking Soda and water, then rinsing after a few minutes. This is thought to neutralize the small amounts  of formic acid released by the tiny, hollow hairs.

# Influence on language and culture
In Great Britain the stinging nettle is the only common stinging plant, and has found a place in several figures of speech in the English language. To "nettle" someone is to annoy them. Shakespeare's Hotspur urges that "out of this nettle, danger, we grasp this flower, safety" (Henry IV, part 1, Act II Scene 3). The common figure of speech "to grasp the nettle" probably originated as a condensation of this quotation. It means to face up to or take on a problem that has been ignored or deferred. The metaphor refers to the fact that if a nettle leaf is grasped firmly rather than brushed against, it does not sting so readily, because the hairs are crushed down flat and do not penetrate the skin so easily. However the sting of nettles has been recommended to relieve the pain of rheumatism as the effects of the sting can last up to twelve hours. The stinging feeling becomes a warm feeling on the area treated so helping the pain of the rheumatism to subside. In the German language, the idiom "im Nesseln gesetzen", or to sit in nettles, means to find oneself in hot water.

# Edibility
Stinging Nettle has a flavor similar to spinach when cooked, and is rich in vitamins A, C, D, iron, potassium, manganese, and calcium. Young plants were harvested by Native Americans and used as a cooked vegetable in spring when other food plants were scarce. A soup made from the young shoots is considered a spring delicacy in Scandinavia. Cooking or drying completely neutralizes the toxic components found in this plant.  Stinging Nettle should not be consumed after it enters its flowering and seed setting stages, as the leaves develop gritty particles called "cystoliths" which can irritate the urinary tract.