The naturally blonde actress has been dying her locks black for her role on the hit police series for the past 11 seasons, but as she was gearing up to return to work after a summer hiatus, the dye she had been using for the past year prompted an unwanted trip to the hospital.
Perrette took to Twitter.com on Friday (18Jul14) to share a photo of herself in a medical gown with a badly swollen face and a nearly fully shut eye.
She wrote, "This was me at hospital today and it got worse #Allergy #AllergicReaction.
"Did my head look a bit puffy on the red carpet last night? Turns out I was having a dangerous allergic reaction to hair dye. Been battling this for a year now but it gets worse every time. It's an acquired allergy for people that dye their hair for years.
"Was in Er. Just got home from hospital. Awful. My head swelled up huge like a melon... Know the symptoms. It can be fatal. People have died. For real."
Hours after the ordeal, the swelling had gone down and Perrette even walked the red carpet with her co-stars at the Television Critics Association summer press tour in Los Angeles.