But when the mole wouldn't stop bleeding she visited her doctor, who diagnosed her with cancer.
After cutting the mole off, dermatologists discovered she had stage three melanoma which had spread to her lymph nodes.
After several operations to remove the nodes, and a 7cm portion of skin, Kat got the all clear.
"A dermatologist said the mole was probably just reacting because I'd nicked it but they removed it to be on the safe side and sent it away for tests. Two weeks later I got a call from my GP telling me it was skin cancer. It was scary," says Kat, from Bristol.
"I'm so glad I spotted the change when I did. It probably saved my life."
Now that's what you call a close shave.
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