Bunion. Close-up of a bunion on the big toe. A bunion is an inflamed fluid-filled pad covering the joint of the big toe. The majority of bunions are caused by the condition hallux valgus. This is where the big toe (hallux) bends inwards, and the joint at its base protrudes, as here. Continued rubbing of this joint on tight shoes leads to inflammation, and bunion formation. Bunions can be very painful, and will grow if correctly fitting shoes are not worn. Shoes which force the big toe into a straight position will help relieve small bunions, but larger ones may require surgery to correct the shape of the joint.