لماذا تصبح أنابيب سماعة الطبيب لزجة؟

I've noticed that the tubing of my stethoscope often gets sticky, and I'm quite puzzled as to why this happens. Could it be due to the material the tubing is made of? Or is it perhaps the oils from my skin that accumulate over time? I've tried cleaning it regularly, but the stickiness persists. Could there be any specific cleaning agents or techniques that could help alleviate this issue? It would be great if you could shed some light on this matter and provide me with some insights on how to keep my stethoscope tubing clean and non-sticky.