ABCDE, the ugly duckling sign and other ways to check your own moles

Check in good light, ideally monthly or every few months. Use a full-length mirror and a hand mirror, or ask a partner to help with your back and scalp. Look at all areas, including between the toes, soles, nails, genitals and behind the ears. Know your normal pattern of moles and take photographs. The aim is to notice change, not to catalogue every mark.

• Asymmetry: one half does not match the other.

• Border: edges are ragged, notched or blurred.

• Colour: more than one colour, or uneven shades of brown, black, red, white or blue.

• Diameter: larger than a pencil rubber is a traditional prompt, though melanomas can be smaller.

• Evolving: any change in size, shape, colour, elevation, or new symptoms such as itching, crusting or bleeding.

Most of a person's moles tend to resemble each other. A mole that stands out as different, whether larger, darker, paler or oddly shaped, is the ugly duckling. Clinicians use this pattern recognition alongside ABCDE. It helps with people who have many moles, where applying ABCDE to each would be impractical.

Nodular melanomas can grow quickly, be firm and raised and may be pink, red or skin-coloured. Amelanotic melanomas lack pigment. Melanomas under nails appear as a dark streak that widens, or nail damage that does not heal. Melanomas on palms and soles can look like bruises or stains. Non-melanoma skin cancers can present as a sore that does not heal, a pearly bump or a scaly red patch. Any such lesion needs assessment.

Many marks look alarming but are benign: seborrhoeic keratoses (stuck-on, waxy brown patches), cherry angiomas (small red dots), freckles and dermatofibromas. Only a trained clinician can be sure. If you are unsure, ask rather than guess.

Take a clear photograph with a scale, note the date and see your GP promptly if the lesion is new, changing, bleeding, itchy or looks different. Do not try to cut, burn or freeze it yourself. If it is bleeding and does not stop, or you have rapidly growing lesions, seek urgent advice. Contact NHS 111 if unsure how fast you need help.

Pick a regular date, such as the first of each month, and photograph any moles you want to track against a plain background with a ruler beside them. Store the pictures in a dated folder. Note anything that itches, crusts or bleeds. When you see a clinician, the sequence of images shows change far better than memory. Ask a partner or friend to photograph your back, and remember that photographs complement, rather than replace, a professional check if you have many moles or a family history.