Would you know what a dark line on your nail means?

Most of us would probably just assume it's bruising under the nail, or a weird sign of a deficiency in calcium.

But in fact, a dark line on your nail can be an indicator of something more serious – and it's a sign most of us would ignore or miss.

Nail artist Lisa Harrison Williams wants to raise awareness of how a dark line on your nail can be a sign of skin cancer, so that no one else delays diagnosis or treatment because of a lack of information.

Lisa had a walk-in nail client, who came in with a dark vertical stripe down her nail.

She asked for a colour that would be dark enough to cover the stripe, noting that previous salons had told her the mark was down to a blood blister or a lack of calcium.

'This is melanoma,' writes Lisa. 'I did not want to frighten her but I told her she needed to see her doctor immediately!'

Lisa advised her client to head to the doctor, where she says she was diagnosed with an aggressive melanoma that had already spread to her lymph nodes.

'Please pay attention to abnormalities in your nail beds,' Lisa urges. 'Odd changes in your nails can very likely be nothing to worry about.

'But sometimes it is an indication of a very serious disease.

'And please keep an eye on the nail beds -toes and fingers – of your elderly loved ones and your loved ones that aren't physically able to notice changes in the nail beds! Early diagnosis can make all the difference in the world!!!'

Lisa isn't exaggerating. While a change in the nail is very often just physical damage, such as bruising, in some cases it can be a sign of skin cancer.

Fiona Osgun, Cancer Research UK's senior health information officer told metro.co.uk: 'Melanoma skin cancer can cause different symptoms, including discolouration under a nail.

'By getting to know what's normal for you – including any lumps, marks or niggles – you're more likely to notice anything out of the ordinary.

'If you do notice any changes anywhere on your skin, whether it's a new mole or mark or something else that's changed, get it checked by your doctor.

'Most melanoma skin cancers develop on the chest, back or legs, occasionally they can appear as discolouration under nails or on the palms of the hands or the soles of the feet.

'It probably won't be skin cancer, but if it is, getting treatment started before it has time to spread can make a big difference.'

In short: Don't descend into panic if you notice a dark mark on your finger or toenail. It's likely nothing, but it's definitely worth going to your GP to get it checked out – if only for your own peace of mind.