Rashes can also be caused by skin irritation, which can have many causes, such as an allergic reaction, or a sting from a plant such as a stinging nettle.

Professor Hywel Williams, from the British Skin Foundation, explains. “Some rashes are genetic, some are caused by things attacking the skin from the outside like insect bites, fungal infections or bacterial infections, some are an indicator of internal illnesses, some develop as a side effect to drugs, and others appear from the inside for no obvious reason.”

But generally a rash is any inflammatory condition of the skin. Some rashes can be a sign of a serious condition, which in very rare cases may be life-threatening. Some rashes are caused by ongoing conditions, such as eczema or psoriasis.

Because the term rash has no precise meaning, but often is used to refer to a wide variety of red skin symptoms, skin specialists (doctors called dermatologists) will often look at the location, appearance and colour of a rash to help them to make a diagnosis.

You can check your skin for any changes yourself, and Professor Williams has some tips on how best you can do this. “Don’t just look at one spot, but look at the whole skin including places you do not normally look, the hair, nails and inside the mouth, even if you don’t have any symptoms in these places.”

And don’t forget about other parts of your ‘skin’, including your hair and nails, which are all made of the same family of fibrous structural proteins called keratin – the key structural material making up the outer layer of human skin. “The skin is all connected, and you might pick up clues by thinking about the skin, hair and nails as one large organ of the body”, Professor Williams says. There are also symptoms checkers available online on the NHS Choices website where you can check any worrying symptoms.

We’ve probably all experienced how annoying itchy skin rashes can be, and remember being told as a child not to scratch to avoid having scars from skin rashes. That advice still holds true, Professor Williams says. “Don’t excavate your skin if it is itchy. Gentle scratching or rubbing without breaking the skin is probably OK.”

Treatment for a rash depends on what has caused it, however if you have concerns seek medical advice. If you are phoning for medical advice, for example on an NHS advice line, be prepared to describe the rash, when it developed and possible triggers.

 “Don’t guess. If in doubt, check it out”, Professor Williams says. Your GP will be able to tell a common skin rash from a more serious skin rash, or refer you to a specialist if this is necessary.