Is it just a few millimeter around the stoma? If so, it might likely be a zone where feces end up touching his skin without actually being a leak per say (for me this only appears on the lower half of my stoma for instance). The acid from the output can easily eat/dissolve the product form the barrier and it can leave enough space to cause that type of irritation. Would you say that it looks like the skin is a bit raw?
If this is similar to what you observe then, the paste and powder strategy might not be enough or last long enough. Ask your son if it itches. I sometimes wait for an extra day before changing my appliance (let say I feel lazy) and when I do so it sometimes end up itching and showing a red zone because the barrier broke. Because I am used to my products and routine I rarely have irritation issues now but I recently started using mouldable Secuplast from Salt to prevent them and it seems last much longer than just the paste that I had stopped using. I make a tiny roll from the disc of paste and snug it to my stoma and then I put the flange and press well all around to assure a perfect seal.
The nurse will likely be able to tell. If she says it's irritated, that strategy might be helpful for you.
