In short
Nerve damage from diabetes starts in the toes because the longest nerves fail first. Why a foot that has stopped hurting is the worrying one, and which foot problems are an emergency today.
Emergency if: Go to hospital now, today, for an open ulcer or sore on the foot; skin on the foot that is red, warm or painful; a foot or toe that is hot, red and swollen even with no wound visible; any discharge, pus or bad smell; tissue that has turned black; a wound with fever or feeling generally unwell; or a foot that has suddenly become cold, pale or dusky and painful. In diabetes with nerve damage these are limb-threatening and they move fast: infection can pass from skin into bone within days, and a hot swollen foot without a wound can be bones collapsing under a numb foot, where every further day of walking costs more of the foot. Do not wait to see whether it settles, do not treat it yourself, and keep weight off that foot on the way in.
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01
Why does it start in the feet, and what does it feel like at first?
Because the longest nerves fail first. The nerve fibres running from the spine to the toes are the longest in the body, and they are the most vulnerable to the metabolic injury of sustained high blood sugar. Clinical reviews describe the result as a stocking-glove distribution developing over several years: the distal sensory and autonomic fibres are damaged first, and the damage then progresses upward. That is why the hands are usually spared until the numbness has already climbed some way up the legs, and why a report of tingling in the fingers with normal feet is more often something other than diabetes.
NIDDK describes the early sensations as burning, tingling, like pins and needles, numb, painful or weak, typically in the feet and legs and sometimes later in the hands and arms. Two details help you recognise it. Symptoms are often worse at night, and most of the time they are on both sides of the body, which distinguishes this from a single trapped nerve. Later signs include changes in the way you walk, loss of balance, reduced muscle tone and swollen feet. NIDDK puts the reach of peripheral neuropathy at about one-third to one-half of people with diabetes, and CDC says about half of all people with diabetes have some kind of nerve damage.
02
Pain or numbness: which one should worry me more?
The numbness, and it is not close. Pain is unpleasant and it is a reason to be treated, but pain still tells you where your foot is and what it has just stepped on. NIDDK puts the danger of numbness simply: if peripheral neuropathy causes you to lose feeling in your feet, you may not notice pressure or injuries that lead to blisters and sores. You may not feel a pebble inside your sock, a nail through a slipper, or a blister forming on a long walk. Diabetes then makes those wounds slow to heal and more likely to become infected, and the end of that road is losing toes, a foot, or part of a leg.
There is a further trap in the sequence. Clinical reviews note that detectable loss of protective sensation tends to occur later in the disease, sometimes even after a neuropathic ulcer has already developed, so the first hard evidence of numbness can be the wound itself. The same reviews report that at five years the risk of death for someone with a diabetic foot ulcer is about two and a half times that of someone without one, which is a measure of how much else is usually going on by the time an ulcer appears. A foot that has stopped complaining has not improved.
03
What exactly am I looking for in the daily foot check?
NIDDK's instruction is to check your feet every day, in the evening when you take your shoes off, and to check between the toes as well. Use a mirror propped on the floor or ask someone else if you cannot bend or see the soles. The list to look for is cuts, sores or red spots, swelling or fluid-filled blisters, ingrown toenails, corns or calluses, plantar warts, athlete's foot, and warm spots. CDC's version adds redness, changes to the skin or nails, colour and temperature changes, dry cracked skin, thickened yellow toenails, and a change in the shape of the foot over time.
The don'ts matter as much as the checklist. NIDDK says not to walk barefoot, and not in socks alone even indoors; not to cut corns or calluses yourself or use medicated corn removal products; and not to use hot water bottles or heating pads on the feet, because a numb foot cannot tell you it is burning. Beyond the daily check, have your feet examined by a professional at least once a year, and more often if nerve damage or any foot problem is already present. CDC puts the same advice as a yearly complete foot exam, more often with nerve damage.
04
Which symptoms are nerve damage that nobody connects to diabetes?
Autonomic neuropathy damages the nerves that run the organs, and its symptoms are usually blamed on something else. In the digestive system it causes bloating, fullness and nausea, constipation, vomiting, and diarrhoea that is characteristically worse at night; gastroparesis is the version where the stomach empties slowly or stops emptying, which also makes blood sugar after meals unpredictable. In the bladder it becomes hard to know when you need to pass urine and when the bladder is empty, leading to urine sitting in the bladder, repeated infections, and incontinence.
Three more are worth naming. Blood pressure control fails, so you feel light-headed or faint on standing up, and the heart may beat fast or irregularly; the same nerve damage can blunt the chest pain that would normally warn of a heart problem. Sexual function is affected: erectile dysfunction and ejaculation problems in men, reduced lubrication and difficulty reaching orgasm in women. And hypoglycaemia unawareness is the most dangerous, where you stop feeling a low blood glucose coming and can reach a severe low or lose consciousness without warning. Heavy sweating at night or while eating, or not sweating at all, belongs to the same group.
05
How is it tested, and what else has to be ruled out first?
The core test is done with your shoes off and takes a few minutes. The doctor is looking for loss of protective sensation, and the standard instrument is a 10 gram monofilament, a nylon strand pressed against defined points on the sole until it bends; not feeling it predicts ulcer risk. A 128 Hz tuning fork held at the joint of the big toe tests large-fibre vibration sense, which most people feel for about eighteen seconds. Pinprick and temperature test the small fibres. Ankle reflexes and light touch are checked too, since reduced light touch and lost ankle reflexes tend to appear earlier in the process. Your gait and balance are watched as part of the same examination.
Blood tests are there to exclude the imitators, and this is the step people skip. Before nerve symptoms in someone with diabetes are called diabetic neuropathy, clinical reviews expect vitamin B12 deficiency, hypothyroidism, alcohol-related neuropathy, the neuropathy of kidney failure and heavy-metal toxicity to be considered. B12 deserves particular attention because long-term metformin use can lower B12 levels, so it needs checking rather than assuming. That is why a sensible workup for tingling feet in diabetes includes B12 and TSH alongside HbA1c, fasting glucose, creatinine and eGFR. Our separate story on tingling hands and feet goes through how those results are read together.
06
What helps the pain, honestly?
Start with what nothing does: no current treatment repairs the damaged nerve. NIDDK is explicit that the medicines used address the pain rather than the underlying nerve damage. What the reviews list first for painful diabetic neuropathy are two groups of medicines rather than any single one: the gabapentinoid anticonvulsants, and one of the serotonin-noradrenaline reuptake inhibitor antidepressants; second-line options include the other antidepressants of that class, the tricyclic antidepressants, and medicated patches applied to the painful skin. Which of these suits you depends on your kidney function, your other medicines and what side effects you can tolerate. Both the choice and the dose are prescription decisions your doctor makes on those grounds - never something to borrow from a relative's tablets, and never an old prescription restarted on your own.
Two honest negatives. Taking oral vitamin B12 supplements has no evidence of improving diabetic peripheral neuropathy when B12 deficiency is not the cause, so supplementing without a measured deficiency is spending money on nothing. And pain relief, however good, does not reduce the risk from the numb areas: someone whose burning feet have been settled by treatment still needs the daily check, the annual foot examination and the well-fitting shoes. The one intervention that acts on the disease rather than the symptom is glucose control over years, alongside blood pressure, lipids and not smoking, and it slows progression rather than undoing what has happened.
07
Which foot problems become an emergency within hours?
An open sore on the foot of someone with diabetes is not a next-week problem. NIDDK says to get medical care right away for a cut, blister or bruise that does not start to heal after a few days, for skin that becomes red, warm or painful as a sign of possible infection, for a callus with dried blood inside it, and for a foot infection that becomes black and smelly, which suggests gangrene. Poor blood flow makes these slow to heal and sometimes unable to heal at all, and infection in that setting can move from the skin into bone and bloodstream in a day.
The trap is a hot, red, swollen foot with no wound at all. In someone with diabetes and neuropathy that picture can be Charcot foot, in which bones fracture and joints collapse in a foot too numb to protest, and it is easily mistaken for a sprain, an infection or a clot. MedlinePlus lists the early symptoms as mild pain and discomfort, redness, swelling and warmth, with the affected foot noticeably warmer than the other, and says to contact your provider if you have diabetes and your foot is warm, red or swollen. Walking on it leads to further bone and joint damage and to the collapsed rocker-bottom deformity that later causes ulcers.
Nerve damage and your feet: when to act
Routine — see a doctor
Book a review with your diabetes team for burning, tingling, pins and needles, numbness or weakness in the feet that has come on gradually, especially if it is on both sides and worse at night; and ask for the sensation tests with the monofilament and the tuning fork if they have not been done. If any part of a foot is already numb, start the daily foot check tonight and stop walking barefoot, indoors included: a numb foot cannot report an injury, so looking at it is the only warning left. Ask at the same visit for a complete foot examination if you have not had one in the past year, and for vitamin B12 and thyroid checks if the tingling has not been investigated - long-term metformin use lowers B12 in some people. Also worth raising without urgency: feeling faint on standing, bloating and early fullness after meals, night-time diarrhoea, bladder emptying that feels incomplete, unexplained heavy sweating at night or while eating, and sexual difficulties. These are commonly autonomic nerve symptoms and are seldom volunteered.
Same-day — call promptly
Call your doctor today for any new break in the skin of the foot - a cut, crack, blister or bruise - even a small one, and for any callus with dried blood inside it, a fungal infection between the toes, an ingrown toenail, or a foot that has changed shape. Same-day also for a cut, blister or bruise on the foot that has not started to heal after a few days. And treat hypoglycaemia unawareness as same-day: if you have stopped feeling low blood glucose coming on, your treatment targets probably need reviewing before the next scheduled appointment, because the next low may arrive without warning.
Emergency — act now
Go to hospital now, today, for an open ulcer or sore on the foot; skin on the foot that is red, warm or painful; a foot or toe that is hot, red and swollen even with no wound visible; any discharge, pus or bad smell; tissue that has turned black; a wound with fever or feeling generally unwell; or a foot that has suddenly become cold, pale or dusky and painful. In diabetes with nerve damage these are limb-threatening and they move fast: infection can pass from skin into bone within days, and a hot swollen foot without a wound can be bones collapsing under a numb foot, where every further day of walking costs more of the foot. Do not wait to see whether it settles, do not treat it yourself, and keep weight off that foot on the way in.
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Sources
- Peripheral Neuropathy - NIDDK (NIH)niddk.nih.gov
- Autonomic Neuropathy - NIDDK (NIH)niddk.nih.gov
- Diabetes and Foot Problems - NIDDK (NIH)niddk.nih.gov
- Diabetic Neuropathy - StatPearls, NCBI Bookshelfncbi.nlm.nih.gov
- Diabetes and Your Feet (CDC)cdc.gov
- Charcot foot - MedlinePlus Medical Encyclopediamedlineplus.gov
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