What Causes Numbness on the Left Side?

A number of different medical problems can cause numbness on the left side, with some being more serious than others. Numbness that lasts more than a few moments should almost always be a cause for alarm, though, as should tingling that occurs over large parts of the body. Strokes, brain tumors, and seizures are some of the main causes of this sort of loss of sensation, but more latent conditions like multiple sclerosis or diabetes might also be responsible. People who regularly feel numb on their left side or who are unable to account for sudden or persistent tingling should usually seek medical attention.

One of the most common causes of numbness anywhere is stroke, which happens when the brain — in part or full — suddenly loses its blood supply. When this lasts for more than a few seconds, the results can be devastating and tend to be immediately noticeable. Smaller strokes can sometimes go undetected at first, though their symptoms and after-effects are usually very apparent. Numbness that is concentrated on one side of the body is often caused by a stroke impacting the part of the brain that controls that side.

The human brain is divided into hemispheres, with the right hemisphere controlling the left side of the body and vice versa. A stroke that impacted any of the major communication zones of the right hemisphere could cause numbness that a person would feel up and down his or her left side. This is particularly true of tingling that happens in multiple places simultaneously, like in an arm, a leg, and shoulder all at the same time.

A brain tumor in the right hemisphere can also cause a slow loss of sensation on the left side of the body, though in these cases the tingling tends to get progressively worse. What may start as intermittent numbness will progress to full loss of feeling. The sooner tumors are identified the better the likelihood that they can be safely removed or neutralized, which makes paying attention to sensation problems really important.

Migraine headaches and seizures are very different from a medical perspective, but both tend to “signal” or forewarn their arrival with symptoms that can include targeted numbness. Timing can vary from person to person, but in most cases numbness comes and goes with about an hour of either a debilitating headache or a brain seizure. It’s rare for this symptom to be long lasting, and treating the root cause usually takes care of it, too.

The blood sugar condition diabetes sometimes causes damage to the central nervous system, particularly when it has gone untreated for a long time. In some cases this damage can lead to numbness that is focused on certain body parts or even entire sides of the body. Patients can usually get rid of this by bringing their blood sugar levels back within normal range, but not always. Diabetics who experience persistent numbness or tingling should usually get a medical evaluation to figure out if their condition is being properly managed.

People who suffer from multiple sclerosis sometimes also experience numbness that is concentrated in certain parts of their body. Most patients report tingling in single places, commonly the hands and feet, at first, but as the condition develops this can spread to entire sides of the body. Multiple sclerosis is a degenerative neurological condition where the protective coating around the body’s core nerves begins eroding over time. The disease can’t be cured, but a number of different medications and lifestyle changes can help patients keep their symptoms, including numbness, under control.

Sitting, standing, or lying in one position for prolonged periods of time can sometimes cause numbness on one side, too. People who have limited mobility or who work in vocations that require staying in one position a long time are usually the most at risk for this sort of numbness, and it’s also a common compliant of long-term care patients and others who are confined to bed for any length of time. Changing position and moving the impacted arm and leg can often help get the blood circulating again, which tends to help things feel normal again; people with mobility issues or who are bedridden for months at a time are usually wise to find caregivers who are able to help them move their muscles every now and then.

Treating numbness on the left side usually requires a varied and somewhat dynamic approach, and typically centers on managing and treating the underlying condition. It is rare for entire areas of the body to lose sensation without some other problem. Sometimes tingling will go away on its own, as is often the case with inactivity, but medical providers usually recommend that anyone who experiences numbness that doesn’t go away, that comes and goes with some regularity, or that seems to get worse over time get help to uncover the root cause.