If you are new to photography, you may not know the bigger the difference between the near distance and the far distance of your subject, the bigger the distortion. That’s why selfies with the forehead close to the camera look like the subject has a giant forehead (and one reason why selfies are often cropped at the forehead).
These distances are also relative, as in being 1/2″ from a 1″ object is not as bad as 2″ from a 6″ object and not as bad as 4″ from a 12″ object as seen here:
You can correct the distortion by backing up and using telephoto focal lengths to frame closer to the subject.
Going from close and wide angle (which includes more of the background) to farther away and telephoto (which compresses the foreground/background) also changes what you see in the background. In the above case, it eliminates the upper corners of the seamless background. (Try to do THAT with “zoom with your feet”.) Below, it eliminated the distracting trees.
This also made the foreground and background more out of focus. Out of focus areas also tend to either lighten or darken based on the predominant tone in the area (in this case, it got lighter).
Or you can take the effect to your advantage and emphasize the close subject while including a lot of background.
Stronger telephoto (above 150mm) is usually fine for all subjects including event photography and full length portraits, but if you are shooting a close-up portraits, be cautious. Above 150-200mm tends to flatten out facial features and give a small-face/big-head effect (sometimes called the Arnold effect). Just Google “impact of focal length on portraits” or visit http://stepheneastwood.com/tutorials/lensdistortion/strippage.htm for a great example. I lean toward 90-100mm (about 60mm on a crop factor sensor) myself.
As the above example shows, you don’t need ultrawide lenses to get distortion. The top 3 images were shot at the 35mm equiv of 28mm which is by no means a fisheye or even an ultrawide lens, but get beyond 10-12mm and you get some serious distortion until you get a round image that goes 180° (and sometimes beyond).