From my own and my DH's experience, they can also be a tell tail sign of some disease. Many years ago DH noticed that he started having a lot of skin tags on his under arms and the front of his body, but after after having a cancerous kidney removed, one day months later he noticed that all the tags were gone. Then I started noticing that I had a lot of them on my under arms and chest, they disappeared after my mastectomy.
I've only spoken to 3 or 4 others who had the same thing happen, which is a small amount of people.
I have spoken to 2 folks who had a lot of them but they went away after they changed their life styles, started being careful of foods eaten and took a lot of coral calcium from Okinawa and quitting smoking.
But I think on the average these are perhaps signs of artificial foods we eat and possibly lack of real vitamins and minerals.
I'm interested in this and will continue to watch it.