What's the difference between photophobia and photosensitivity? To a person who is sensitive to light, there is no difference!
Photophobia and photosensitivity both mean that a person perceives light as brighter than it is and/or has a sensitivity to light that may or may not cause pain. In either case, light can trigger symptoms of an existing condition like migraine, blepharospasm, Sjogren’s syndrome (and many others, here's a comprehensive list). But even a person who is otherwise healthy and has no underlying condition can feel ill due to light, especially fluorescent lighting.
In a person’s practical experience, photophobia and photosensitivity mean the same thing, but they technically have different definitions. Photophobia literally means “fear of light.” It is used in medicine to mean an aversion to or avoidance of light, whether light is painful or not. Photosensitivity can mean any sort of reaction to light, but in medicine it is primarily used to mean skin reactions to light.
Some people use photosensitivity instead of photophobia to avoid the inference of fear. Primarily, though, the difference is seen in traumatic brain injury (TBI) research. TBI researchers have chosen to use photosensitivity because photophobia can mean inflammation of the eye, which is not seen in people who are sensitive to light due to TBI.1,2 This gets confusing, however, when you consider that many conditions that include a light sensitivity component are not accompanied by eye inflammation.
Another key difference is photosensitive epilepsy, in which flashing lights and other light sources can cause seizures. Although a person with this type of epilepsy may be sensitive to many forms of common lighting, the condition is typically triggered by specific patterns, speeds and/or contrasts of light.
Photophobia is far more commonly used to describe a visual sensitivity to light and it’s the term that’s usually the most fruitful in online searches. The exception is for TBI and concussions as well as epilepsy, where photosensitivity is more commonly used word. As no medications exist for photophobia, precision tinted glasses remain one of the most effective natural treatments for photophobia to bring relief for painful light sensitivity.
Du, T., Ciuffreda, K. J., & Kapoor, N. (2005). Elevated dark adaptation thresholds in traumatic brain injury. Brain injury, 19(13), 1125-1138.
Kapoor, N., & Ciuffreda, K. J. (2002). Vision disturbances following traumatic brain injury. Current treatment options in neurology, 4(4), 271-280.