Sensitivity to light is the inability to tolerate light, medically known as photophobia. In someone who is light sensitive, any type of light source (sunlight, fluorescent light, incandescent light) can cause discomfort. Photophobia typically causes a need to squint or close the eyes, and headache, nausea, or other symptoms may be associated with photophobia. Symptoms may be worse with bright light. Light sensitivity is caused by a number of conditions that affect the eye (such as iritis, uveitis, and keratitis), as well as conditions that affect the entire body.