How much bacteria your fingernails contain compared to a toilet seat, depends largely on nail biting habits, hand hygiene and how often the toilet seat is cleaned. Illness causing germs have been found on people's fingernails, with the most likely causes being handling meat, poor bathroom hygiene and changing diapers.
Recent research showed that from a sample of 100 men and women, potentially harmful bacteria were found on 24 percent of the men's nails and 15 percent of the women's nails. The reason that hands and fingernails are dirty is that hands are used for almost everything, and they come into contact with many different surfaces. Fingernails are usually even dirtier than fingers since bacteria can become trapped underneath them and fingernails can be harder to clean as frequently without using a special brush.
Many people are prone to biting their nails, and this is another source of bacteria. It is possible to transfer the germs into your blood stream during nail biting, especially if the nails are sharp enough to cut the gums. Toilet seats can have billions of bacteria living on the surface as the water from the bowl can evaporate and settle on the top of the toilet seat. However, frequent flushing and cleaning help to reduce this.