A sore that will not heal: causes, red flags and when to get it checked

Healing needs good blood supply, a clean wound bed, adequate nutrition and a working immune system. A wound that stalls signals a problem with one of these, or a tissue that is not behaving normally, as in a skin cancer, which grows rather than heals.

• Chronic wounds from pressure, friction or repeated injury, and poor wound care.

• Venous leg ulcers: shallow, wet ulcers above the inner ankle with swelling, varicose veins and skin discolouration.

• Arterial ulcers: painful, punched-out sores on toes or heels, with cold feet and weak pulses, common in smokers.

• Diabetic foot ulcers: often painless because of neuropathy, on pressure points of the foot.

• Infection: bacterial, fungal or, in some travellers, unusual infections including leishmaniasis.

• Skin cancer: basal cell carcinoma (pearly, rolled edge, bleeding), squamous cell carcinoma (scaly, crusted, firm), and melanoma.

• Inflammatory conditions such as pyoderma gangrenosum, vasculitis and sickle cell disease.

• Nutritional deficiencies, steroid use and radiation damage.

A sore with a raised pearly or crusted edge, easy bleeding, rapid growth, a sore on sun-exposed skin, lip or ear, a foot sore in diabetes, black or dusky tissue, spreading redness, fever, pus, severe pain, and a sore with swollen lymph nodes need prompt assessment.

• A&E or same-day GP: spreading redness, fever, a foot sore in someone with diabetes, black tissue or severe pain.

• Urgent GP referral: a persistent sore with features of skin cancer.

• GP within days to weeks: any sore not healing after about four weeks.

• Practice nurse or pharmacist: a small new wound for dressings and advice.

The doctor asks how long, how it began, injury, pain, discharge, diabetes, smoking, circulation, medicines, sun exposure and previous skin cancers. They examine the sore, surrounding skin, pulses, sensation, leg veins and lymph nodes, and may measure ankle-brachial pressure.

• Wound swab: if infection is suspected.

• Skin biopsy: the key test for suspected skin cancer or inflammatory ulcers.

• Blood tests: glucose or HbA1c, full blood count, kidney function, albumin and inflammatory markers.

• Ankle-brachial pressure index and Doppler: to assess arterial supply before compression.

• Imaging: X-ray or MRI of the foot if bone infection is possible.

Keep wounds clean and covered with an appropriate dressing, avoid picking, and protect from pressure. Stop smoking, control blood sugar, eat adequate protein and elevate swollen legs. Compression therapy is effective for venous ulcers, but only after arterial disease has been excluded. Do not apply unproven remedies to open wounds.

The NHS route is a GP, practice or district nurse, podiatry or tissue viability, with dermatology for suspected cancer. Private dermatology, podiatry and leg ulcer clinics offer direct access to biopsy and dressings.