I've recently noticed that my nipples have this puffy look when they're warm, but they seem perfectly normal and even shrink when it's cold. I'm 23 and this really makes me hesitant to take off my shirt around others. There's no lump under my nipples, so I know it's not gynecomastia. I'm wondering if there's any way to get this sorted out for good. Could you please shed some light on this?

It sounds like you're experiencing temporary nipple puffiness, which is usually normal and not a sign of any underlying condition like gynecomastia. Since there are no lumps and no pain, this could simply be a natural response to temperature changes. If it causes significant distress, you may consider consulting a doctor for reassurance or potential treatments like surgery if needed.