The problem is that there are quite a few which superficially look as though they might sting you but are actually harmless.
This is a slide show which separates the stingers from the non stingers.
YESThe leaves and stem are covered in hairs some of which (trichomes) are hard, sharp and act as hypodermic needles. They easily penetrate skin and deposit a cocktail of chemicals including histamine. This produces a form of dermatitis which is known as Stinging Nettle Rash.
Urtica dioica as its name suggests, is dioecious having female and male flowers on different plants. It is a native, perennial plant which will grow almost anywhere and is often found as a tall herb on roadside verges which which have absorbed soluble fertiliser chemicals from nearby fields (eutrophication).
The negative effacts are well known but it is also the food plant for the larvae of the Peacock and Tortoiseshell Butterflies and several moths.
YESLike Urtica dioica this plant has a mixture of ordinary hairs and trichomes. The trichomes can inject irritant chemicals just like Common Nettle.
By reputation, the sting from Urtica urens is worse than from Urtica dioica but, in my experience, less likely to happen.
It prefers nutrient rich soils so can be a persistent weed near farmyard compost heaps and on allotments.
It is a monoecious (male and female flowers on the same plant) annual plant. It is an archaeophyte which means it was probably introduced to Britain before 1500 AD and now behaves like a native plant.
NOThis is a common plant of waste ground and roadside verges and the leaves look very like those of Common Nettle Urtica dioica.
It is hairy but there are no stinging hairs (trichomes).
Unlike Small Nettle and Common Nettle the flowers are quite prominent.
NOThe edges of the leaves are rounded (crenate) and overall it is a much smaller plant than either Small Nettle or Common Nettle.
It is covered in hairs and is a member of the Dead-nettle family: Lamiaceae, which is maybe enough to put people off touching it.
Lamium purpureum will continue to flourish and flower in winter when the weather is mild so is more obvious when all competitors from Summer, Spring and Autumn have died.
NOThis plant is often confused with Lamium purpureum and often grows in the same places.
The hairy leaves are more serrated (jagged, saw toothed) than in Red Dead-nettle so can lead you to wonder if it stings.
It is nowhere near as common as Red Dead-nettle and quite a shy flowerer, producing very few fully developed flowers in the winter months.
NOLamium maculatum is a garden escape and fortunately easy to identify.
The leaves have distinctive white blotches or stripes on them. It is hairy but there are no stinging hairs.
NOLamium amplexicaule is an introduced annual plant (archaeophyte = before 1500 AD) with ordinary hairs, no stinging hairs and rounded leaf edges.
It is much smaller than Small Nettle and Common Nettle.
It is very common on the continent of Europe and grows much taller and more vigorously than in Britain or Ireland.
NOUnless you live in the far north of Scotland this is unlikely to be a problem for you.
But it does have serrated leaf edges which look to the uninitiated as though they might present stinging hairs.
It thrives in similar habitats to Red Dead-nettle which also grows this far north.
NOThis plant is as tall as Common Nettle, has serrated leaf edges like Common Nettle and is covered in hairs, none of which are stinging hairs.
Nevertheless this is a plant which looks as though it might sting you.
Take a leaf and crush it in your fingers. Now take a deep sniff. You won't forget the smell.
The hoverfly just happened to be passing when I clicked the shutter.
NOMarsh Woundwort tends to have much longer leaves than Hedge Woundwort but still has serrated edges and hairs which seem to threaten stings.
As the name suggests it grows in boggy or wet places but if you crush the leaf and sniff, the smell is similar to but not as strong as Hedge Woundwort.
NOThe quite prominent saw-toothed edge to the leaves and the hairs again suggest that it might sting but it doesn't.
It is a native plant of the woodland and not to be confused with the similar invasive garden plant Lamiastrum galeobdolon ssp argentatum which has mottled leaves and will grow in the open as well as shade.
Some texts will refer to this as Lamium galeobdolon but Clive Stace in New Flora of the British Isles Edition 4, suggests that the microbiology which was used to suggest the name change is not unequivocal and could equally support the original name above: Lamiastrum galeobdolon.
So we stick with the old name.
NOThe leaves of Garlic Mustard really do look similar to those of Common Nettle but are a bright green colour compared with the duller green of Urtica dioica.
Alliaria petiolata flowers in April in hedegrows in similar habitats to Common Nettle (in the countryside) so the two can be seen growing next to each other.
The only confusion might arise before flowering but as soon as the terminal flowerhead on Garlic Mustard blooms there is no mistaking it for Common Nettle.