“The patch” is a transdermal (through the skin) method of using birth control. This method is an alternative to other methods made especially for those who do not prefer pills, vaginal rings, intrauterine devices, injections or implantations. When the patch is applied to your skin, the hormones estrogen and progesterone move from the adhesive on the patch, through your skin and into your body. Your body then knows that estrogen and progesterone are coming from somewhere else (the patch), so your ovaries do not need to release those hormones.
While using the patch, your hormones temporary go to sleep. While they are "napping," they do not release hormones, and do not cause the release of an egg, which is a major way that the patch works to prevent pregnancy. Forgetting to replace the patch as suggested can cause the ovaries to "wake up." When that happens, the ovaries release hormones and may release an egg, which can cause women to get pregnant.