Numbness on the epidermis of the left thumb is caused by the following reasons: 1, due to lumbar spine disease, when the lumbar spine disease, often compress the sciatic nerve to cause numbness in the lower limbs, when the nerve compression is relatively mild, there will also be numbness on the epidermis of the left thumb, such as herniated disc, bulging disc, lumbar compression fracture and other diseases can cause. 2, numbness on the epidermis of the left thumb, there are also The left toe is numb, but it may be a sign of peripheral neuritis, such as suffering from diabetes or taking certain drugs that can cause nerve damage. The numbness of the skin on the left big toe may also be a sign of peripheral neuritis, such as diabetes or taking certain drugs that cause nerve damage after the appearance of peripheral neuritis symptoms, should identify the cause for symptomatic treatment.