Diabetes is the single most common cause of peripheral neuropathy worldwide. Persistently high blood sugar damages nerve fibers over time, and up to 35% of people with type 2 diabetes already show signs of nerve damage at the time they’re first diagnosed. That said, neuropathy has dozens of possible triggers, and in 25% to 46% of cases, no cause is ever identified even after thorough testing.
Why Diabetes Leads the List
Nerve fibers are delicate structures, and they’re especially vulnerable to the chemical environment created by chronically elevated blood sugar. When glucose levels stay high for months or years, the excess sugar triggers a cascade of damage inside nerve cells. The most important of these is oxidative stress, a state where harmful molecules called reactive oxygen species overwhelm the cell’s natural defenses and injure its internal machinery.
One key pathway works like this: excess glucose gets converted into a sugar alcohol called sorbitol inside nerve cells. Sorbitol can’t easily escape through cell membranes, so it builds up and disrupts the cell’s fluid balance. At the same time, the chemical reaction that produces sorbitol uses up a protective molecule the cell needs to neutralize toxic byproducts. With those defenses depleted, the nerve cell becomes increasingly vulnerable to damage from the inside out.
High blood sugar also causes sugar molecules to stick to proteins in and around nerves, forming compounds that stiffen tissues and trigger inflammation. Over time, these overlapping processes degrade the protective coating around nerve fibers, slow down nerve signaling, and eventually kill the fibers themselves. The longest nerves in the body are affected first, which is why most people notice symptoms starting in the feet and working upward.
What Neuropathy Feels Like
The hallmark symptom is numbness, tingling, or a “pins and needles” sensation in the hands or feet. Some people describe burning pain, sharp electric jolts, or a feeling like wearing invisible socks or gloves. Others lose the ability to feel temperature changes or light touch entirely. Because the damage usually starts in the longest nerves first, symptoms almost always begin in the toes and feet before progressing to the fingers and hands.
Motor nerves can also be affected, causing muscle weakness, cramping, or difficulty with balance. When autonomic nerves are involved (the ones controlling involuntary functions), you might notice digestive problems, dizziness when standing up, changes in sweating, or sexual dysfunction. The combination and severity of symptoms depend on which nerve fibers are damaged and how far the condition has progressed.
Other Common Causes
While diabetes accounts for the largest share of identified cases, many other conditions damage peripheral nerves.
Alcohol use. Chronic heavy drinking is one of the more frequent causes. Alcohol is directly toxic to nerve fibers, and heavy drinkers often have poor nutritional intake, compounding the damage. Alcoholic neuropathy typically develops over years to decades, though the timeline varies based on how much someone drinks daily.
Vitamin deficiencies. B12 is critical for maintaining the protective sheath around nerves. When levels drop too low, that sheath breaks down and nerve signals misfire or stop entirely. B12 deficiency is common in older adults, people taking certain acid-reducing medications, and those following strict vegan diets without supplementation. Deficiencies in B1, B6, and vitamin E can also contribute.
Autoimmune conditions. The immune system sometimes attacks nerve tissue directly. Guillain-Barré syndrome causes rapid-onset weakness and numbness, often triggered by an infection with bacteria like Campylobacter (a common cause of food poisoning) or viruses like cytomegalovirus. A related condition called chronic inflammatory demyelinating polyneuropathy (CIDP) develops more slowly and persists for months. Lupus, rheumatoid arthritis, and Sjögren’s syndrome can all damage nerves as well.
Chemotherapy. Many cancer treatments are directly toxic to peripheral nerves. Taxane and platinum-based drugs are the most likely to cause nerve damage, but several other classes carry the risk too. About 68% of people experience neuropathy symptoms one month after completing chemotherapy, and 30% still have symptoms six months or more later.
Infections. Shingles can leave lasting nerve pain in the area where the rash appeared, a condition called postherpetic neuralgia. HIV damages nerves both directly and through the medications used to treat it. Lyme disease, hepatitis B and C, and leprosy are other infectious causes seen worldwide.
Physical compression and injury. Carpal tunnel syndrome is the most familiar example: a nerve gets pinched or squeezed in a tight space, causing pain and numbness in its territory. Herniated discs, repetitive motion injuries, and fractures can all compress or sever nerve fibers.
Toxin exposure. Heavy metals like lead and mercury, industrial chemicals, and certain medications beyond chemotherapy (including some antibiotics and heart drugs) can poison nerve cells.
When No Cause Is Found
Even after a full workup including blood tests, nerve conduction studies, and imaging, somewhere between 25% and 46% of neuropathy cases remain unexplained. These are classified as idiopathic neuropathy. Most idiopathic cases involve sensory nerves and follow a slowly progressive pattern starting in the feet. Some researchers suspect that undiagnosed prediabetes, subtle metabolic disturbances, or genetic factors account for a portion of these cases, but for many people, the cause simply remains unknown.
Idiopathic neuropathy tends to progress more slowly than diabetic or autoimmune forms, and treatment focuses on managing symptoms, particularly pain and balance problems, rather than targeting an underlying disease.
Risk Factors That Overlap
Many causes of neuropathy don’t act alone. Someone with diabetes who also drinks heavily faces compounded nerve damage. A person undergoing chemotherapy who also has a B12 deficiency will likely develop worse symptoms than someone with adequate nutrition. Obesity, smoking, and kidney disease all increase the risk of nerve damage or accelerate it when another cause is already present.
Blood sugar control is the single most protective factor for the most common form. In people with diabetes, keeping glucose levels within target ranges significantly slows the progression of nerve damage and can reduce symptoms. For other causes, the approach varies: stopping alcohol use, correcting a vitamin deficiency, or treating an autoimmune condition can halt or partially reverse nerve damage, especially when caught early. Nerves regenerate slowly (about an inch per month), so recovery after the underlying cause is addressed often takes months to years, and some damage may be permanent.