Sores have hundreds of possible causes, many of which are hard to pinpoint and even harder to shake. Quite often it is the latter. Any of these bites and burrows can become infected, making the sores even more pronounced. And don't forget germs. The most common and contagious of these are bacteria.
Viruses are responsible for such sore-sprouting diseases as chickenpox, herpes, shingles and warts.
Finally, fungi are little invaders that produce such unsavory skin conditions as athlete's foot, jock itch and ringworm. Many skin conditions can develop sores and pustules if they get infected. But infectious agents aren't the only culprits that make sores. Things like age spots or cysts form benign skin growths. A precancerous lesion with the potential of becoming a true skin cancer may first appear as a tiny sore.