Stirling Gallacher has to wear a wig on 'Casualty' because she is "severely allergic" to hair dye.
Stirling Gallacher as Ffion
The 49-year-old star wanted to have red tresses in her role as Ffion Morgan on the BBC medical drama to ensure the character didn't look the same as her 'Coronation Street' alter-ego Paula Martin while she juggles the two roles, but she was unable to dye her locks.
She said: "When I went into 'Casualty', I wanted to make sure that Ffion looked as little like Paula as she could - which is why my hair is now red.
"Well actually, it's a wig, as I'm quite severely allergic to hair dye.
"It's a real bummer, because I love colouring my hair."
Stirling admitted having red hair as Ffion has helped her "both visually and physically" to play the part.
She said: "I think that transformation is useful for me both visually and physically.
"It's important for the audience as well - I don't want them to constantly feel as if they're looking at somebody they were watching on the telly yesterday."
Despite playing both roles at the same time, the 'Corrie' star insists it is easy for her to get to Casualty's Cardiff studios and Corrie's Manchester-based cobbles.
Speaking to Inside Soap magazine, she added: "That's the plan - to keep riding the wagon until the wheels fall off.
"Luckily, I can drive to Cardiff, where 'Casualty' is filmed, and the 'Corrie' studios in Manchester from my home in the Cotswolds.
"They're very slick shows, and both roles are really different, so that makes it easy to dip in and out of each."