What are the symptoms of a disease that seems harmless but can cause death easily?

If you see this pattern on your nails, you should immediately go to the hospital because this is one of the symptoms of an aggressive cancer called melanoma.  If not treated immediately, the chances of survival are low.

"Dark lines on the nails should not be ignored because they can be an indication of subungal melanoma, a type of skin cancer that attacks the bottom of the nail. If you see them, you should see a doctor to check if it is melanoma or not.

"Subungal melanoma usually affects only one nail," explains the NHS. "This cancer will also change the appearance of the line such as becoming wider or darker."

Melanoma accounts for four per cent of all cancers in the UK and has become 119 per cent more common since the early 1990s, according to Cancer Research UK.

Symptoms can appear anywhere on the body, including under the fingernails, between the toes and on the head.