Every now and then a little red dot will show up in a fresh egg. This is a bloodspot. Bloodspots are caused by abrasions or other irritation in the hen’s oviduct.
Contrary to what most believe, a bloodspot does not indicate fertilization. Fertilization can only occur when a male chicken has access to the laying hens. Eggs are laid whether a rooster is present or not, and can contain bloodspots whether fertilized or unfertilized. While we don’t have a rooster, and thus don’t have fertilized eggs, we’ve read that a fertilized egg that has been refrigerated since the day it was collected will not appear or taste any different from an unfertilized one.
Commercial eggs are candled with special equipment to find problems, including blood spots, and any abnormal eggs are discarded. Even commercial eggs occasionally slip through with a blood spot. These are rarely noticed because commercial eggs are usually at least 4 to 6 weeks old by the time they reach the store, and as the egg ages the color of the spot becomes less vivid and thus less noticeable.
Bloodspots can be unappetizing, but aren’t a problem and the egg is still fit to eat. They can either be ignored or gently picked out with the tip of a knife.
For more detailed information about bloodspots, Storey’s Guide to Raising Chickens has some excellent information.