Around age 40, you should go and see a dermatologist for the first time and have a full skin check. At that point, they can review with you anything that looks suspicious or worrisome so that you're aware of what to look for. When you do do a skin exam you want to stand in front of the mirror and go from the face down, looking at everything and seeing if its changed. You should do this maybe once every month to once every two months. Then you can turn around and look at your back in the mirror. Obviously if there's someone that's with you that can look at your back they can do that as well.