The average price of a dozen large, grade-A eggs was $4.15 in December, up from $3.65 in November, according to the Bureau of Labor Statistics. Egg prices were also up more than 36% year-over-year in December, according to the Consumer Price Index.

An ongoing bird flu epidemic has forced farmers to kill millions of egg-laying hens, leading to a serious shortage. The low supply of eggs means customers end up paying quite a bit more than usual at the supermarket. In some places, eggs now cost more than double what they did six months ago.