Why is carpal tunnel worse at night?

Carpal tunnel symptoms are often worse at night because the pressure inside the carpal canal rises when the wrist is bent, and sleep can keep the wrist in one position for hours. The clearest measurements come from wrists held in set positions, not from sleep itself, so the full explanation is an inference. The practical response is to keep the wrist straight through the night, which is what a night splint is designed to do.

The carpal canal pressure rises most when the wrist is bent

The most direct measurement is a 1981 study that placed a wick catheter inside the carpal canal of 15 patients with carpal tunnel syndrome. With the wrist in neutral position, the mean pressure was 32 millimeters of mercury ¹. With the wrist bent 90 degrees toward the palm, it rose to 94 ². With the wrist bent 90 degrees back toward the forearm, it rose to 110, the highest reading in the study ³.

The control subjects, who did not have the condition, showed far lower pressure with the wrist in neutral position ⁴. The comparison matters because it shows that the pressure in patients was raised, and that bending the wrist raised it further.

These are wrist positions held for measurement in a small group, so the study shows how much wrist position changes the pressure. It does not show how much that adds up over a full night of sleep.

Night numbness is the usual pattern

The numbness of carpal tunnel syndrome is mainly felt in the thumb, index, middle and ring fingers, and it often wakes people from sleep, according to the American Academy of Orthopaedic Surgeons ⁵. Because the numbness often comes at night, waking with it regularly is a pattern worth raising with a clinician.

Fluid retention may add to the picture

In a Dutch cohort of 639 pregnant women, higher fluid retention was significantly related to carpal tunnel symptoms, with an odds ratio of 1.8 ⁶. That study followed pregnant women, and it does not measure what happens at night in other adults, so it should not be read as proof that fluid explains night symptoms in general.

Some night numbness has a different cause

A Taiwan hospital review of patients with suspected carpal tunnel syndrome or neck nerve problems found that 20 percent had carpal tunnel syndrome alone, without a neck nerve problem ⁷. Hospital patients are not typical, but the review shows that numbness that wakes you can come from the neck as well as the wrist. That is one reason a clinician may examine both when the pattern is unclear.

What helps at night

1. Keep a short log. Note which fingers are affected, what time you wake, and how the hand was positioned. These details help a clinician decide which tests make sense.
2. Use a night splint. The NHS advises wearing a wrist splint at night to relieve pressure on the nerve, and says you may need up to 6 weeks before it starts to feel better ⁸. The best brace for carpal tunnel covers how to choose one.
3. See a clinician if the waking continues. If numbness wakes you regularly, or your grip starts to weaken, get the wrist examined. The guide to carpal tunnel treatment sets out the options, from splints and exercises to injections and surgery.

Related questions

Daytime typing is covered in can typing cause carpal tunnel syndrome. Pregnancy is a common cause of night symptoms, and the question of whether they last is answered in does carpal tunnel go away after pregnancy. The nerve involved is the median nerve, and the full overview is in carpal tunnel syndrome: symptoms, causes and typing within our speech to text for accessibility, RSI and disabilities section.