The main theme of the aura is supposed to be ruin and entropy.
It hastens destruction and decomposition caused by wear over time.
Metal rusts, stone erodes, plants rot, circuits short out.

I guess it speeds up the effects of time. And it doesn't break down molecules unless they would break down by themselves over time.
That would imply diseases have a faster and more aggressive effect as long as there is a host body to suffer it.
Faster incubation time, increase in severity of symptoms.
Disease outside a suitable host would however starve and become inert quicker.

Biological poisons decay, metal based poisons don't.

On living creatures this power would have a similar decaying effect, aka aging.
However, I made a specific downside for just that reason: the power is psionic based, to be resisted through willpower.
A living creature can resist the effect for some time. 
Creatures that get more powerful over time might even find they grow faster from large amounts of exposure?

So his presence isn't lethal to people, though their smoking habit is even less healthy, and wearing a belt of grenades might be a bad idea.