The most common reason for a painful big toenail is to suffer from onychomycosis. Inflammation of the nail is a common condition caused by a number of reasons, such as puncture wounds, abrasions, and ingrown nails in the nail groove and nearby tissues. These causes can lead to localized Staphylococcus aureus infections in the nail folds, resulting in inguinitis. In the early stage, there may be redness, swelling and pain on one side of the nail groove, and in severe cases, it may spread to the under-nail, thus forming an under-nail abscess, which will cause more severe pain and more obvious symptoms. In the early stage of inguinitis, hot compresses, physiotherapy, topical compresses and other measures should be applied to treat the condition, and antibiotics should be applied to control the infection. If an abscess is formed, surgical treatment is also needed to incise and drain the abscess cavity and remove the nail.