Right off the bat, I'd ask you what software you're using, and what file format are you saving in?
Based on the picture I am assuming that you are saving out JPEGs, because of the compression artefacts. JPG is what's known as a lossy format (as opposed to a lossless format). Every time a JPEG image is saved, compression algorithms are run to reduce the file size. This means that some data is lost every time you make a change to the photo and save it. Ergo, if you save your initial file as a JPG, without leaving access to the original PSD or XCF file, then every time you edit and re-save the JPG, you will continue to lose sharpness, color value, and definition data. If you do have access to the original work files, then I highly suggest saving out with maximum quality, or using the PNG format instead.
Now, if that is not the case, then feel free to correct me.