Injuries and other conditions can be healed by a Medic. Build a Medic's Tent and have it staffed to treat this injury as soon as possible. Conditions cause health loss and other negative effects if left untreated.
Meds greatly increase the speed of recovery and are automatically used directly from the Warehouse when available. Medicine helps with the Injured condition, Iodine Pills with Radiation Sickness and Antibiotics with Infection.
Specialists are not invincible. They can get hurt in combat against bandits, or when they encounter hazards while scavenging and researching locations.
Healing can be only done in the colony. To heal injured specialists, order them to travel back to the colony. They start to heal automatically along the way. Their recovery speed depends on how badly they're injured and how high is their Recovery value is. More information about healing values are found in the Specialist Skill chapter.