"It - depends - it can be either? It's like...a kind of light you can't see, like the part of sunlight that gives you a sunburn but even more than that, it goes through your body - it's how we take the pictures inside people's bodies, actually, though that's a very small controlled amount - and if it's too much then it kind of...burns all of your cells on the inside? It damages the tiny parts that cells need to work and make the right proteins," huh Celestial has a word for 'proteins', neat!, "and to make copies of themselves so your body can heal and maintain itself. And there are kinds of - rock, or metal - that keep releasing the light all the time, and someone's body can be contaminated by that - we're going to check, we can detect the light - but Dr Harrison thinks it isn't based on the description of the attack."
Marian really hopes he's right! She does not want to get cancer!
"...Anyway, the difference there is really mostly whether we're in danger and need to protect ourselves from it - it still kills people by burning inside cells, whether he's contaminated with it or was just exposed to the source at the time slightly changes the treatment but getting it out of him wouldn't get rid of the damage it already did, and apparently a Cure won't fix all of it either. It seemed like it was fixing the - large scale tissue damage? But not the very small cell parts damage..."