The image on the left is a portion of the original.
Its mirror image on the right shows the results of repeatedly saving a JPEG file.
While opening and closing a JPEG file has no effect on image quality, each "Save" as a JPEG file loses some image quality, because JPEG uses "lossy" compression. To maintain the original image quality, use the JPEG file from your camera only as the original. Save the results of any image editing done to the original as a new file, rather than saving it back into itself.
Shown at 3 times normal size, the right-hand image was saved into itself a total of 10 times at 25% quality to dramatize the negative effect on image quality. But, as shown by the previous image (the full-size image of this right-hand portion), even this significantly lower quality is hardly noticeable on the web at normal viewing size.