Swelling and pain on the side of the toenail of the big lesser toe may be caused by acute injury, gingivitis, purulent toe inflammation and other factors. 1. Acute injury: the foot big lesser toes part suffered acute injury, such as heavy objects smashed or excessive pressure, resulting in big lesser toes toenail local damage, will cause lateral swelling and pain symptoms, and may also be accompanied by subnail bruising, toe bone fracture and so on. 2. Nail groove inflammation: usually associated with a variety of factors, such as trimming toenails, skin barbs, knife cuts, etc., can lead to damage to the nail groove and the nearby tissues, resulting in infection, which will lead to swelling and pain in the lateral side of the toenail of the big toe of the lesser toes, and localized redness and warmth and other symptoms. 3. Purulent toe inflammation: may be related to infection, trauma and other factors, can lead to the foot big lesser toes suppurative infection, can cause lateral swelling and pain, with the aggravation of the infection, the symptoms of pain will become more and more serious, and may even lead to local ischemia, necrosis. Swelling and pain on the side of the big lesser toe toenail of the foot, it is recommended to consult a doctor for appropriate examination and treatment to avoid inducing other complications.