Actress Pauley Perrette is struggling to keep her NCIS character dark haired after discovering she has developed an allergy to black dye.

The natural blonde has played quirky Abby Sciuto in more than 250 episodes of the popular Tv show, and now she is having to rethink her character's look after she was hospitalised for an allergic reaction.

She tells U.S. news show Extra, "I have acquired an allergy to black hair dye, which is something that I wanted to tell people about. I tweeted about it, and then it was all over the news because people don't know about it and it can be fatal. It's very serious."

Perrette insists giving up the dye and letting her character go blonde is not an option: "I just don't think Abby should be blonde... Abby's like a cartoon character, she's never changed.

"I have black hair spray in my hair and we're trying to figure it out. We're trying to figure out an organic thing."