The painful pressure on the nail cap of the big toe may be related to the following causes: 1. There may be damage around the nail groove and nail bed. This is most often caused by bunions or tight shoes, which can lead to prolonged compression and friction, resulting in damage to these areas. It is also common for the nail to be inadvertently lifted by a foreign object, causing some degree of damage to the nail bed. 2. It may be caused by infection around the nail, such as a severe fungal infection around the nail, or a gray nail, which may cause damage to the nail and lead to pain. In addition, if there is trauma to the nail, it is very easy to develop a bacterial infection and cause severe pain. 3. This condition may also be caused by bleeding from the nail bed. This bleeding is often caused by excessive activity or the foot being stepped on by others, causing internal bleeding and resulting in pain. 4. It is also common to see lesions of the toe bone, such as fractures of the toe bone or osteomyelitis, which may also cause the above symptoms.