Nanoparticles. They irritate your lungs in ways that are very similar to asbestos irritation. And of course, it's your body's reaction to the irritation that kills you.
Well, that a cream, not dust. So is more of a skin issue, so then the question there is whether it penetrates the skin and turns out to do stuff to the tissue underneath.
I guess that the problem with a lot of these things is that we don't have good (enough?) predictive models for long-term damage.