After more than 30 years of helping patients with skin concerns, there's one conversation I find myself having again and again — the one most people feel too embarrassed to start.

As we grow older, our skin changes. Around age 40, a compound called 2-nonenal starts to appear in the body. It develops as skin oils oxidize, creating a lingering odor that can smell slightly greasy or grassy.

You might know it as "old person smell." This scent is well known in Japan, where it’s called kareishu. It's not a result of poor hygiene. In fact, regular soaps often don't remove nonenal well because it's oil-based and tends to cling to the skin. That's why many people feel frustrated — doing everything right, yet still noticing a persistent odor.

Another reason nonenal is so difficult to deal with is that you often can't smell it on yourself. Your nose adapts to your own scent over time. But the people around you — your friends, your children, your grandchildren — may notice it before you do. And most of them will never tell you.

I've seen patients become emotional in my office when they finally understand what’s been happening. That's exactly why I'm writing this.