It sounds suspiciously like the areas you are seeing are common warts.
If you are in doubt about this, your doctor can easily diagnose common warts just by looking at them. They are caused by a virus, and are spread by person to person contact. Most commonly they are on your hands and fingers, but they can spread to other body areas as well.
There are a number of over-the-counter remedies for warts. They work for many people, but take some time and persistence. You can try these, and if they do not work, you can see your doctor for more aggressive treatment if you want them removed. Generally, warts will resolve themselves within 2 years (yes, years), or so, but many people like to remove them for cosmetic reasons and to prevent spread.
Until they are resolved or removed, keep in mind the virus (HPV, or human papilloma virus) can be spread to other people with skin to skin contact, or even if someone uses a towel after you.
Here is a link with more information: Common Warts