It might be helpful to determine if you have a full fledged mental condition or a fixation on a particular element. A mental condition might require medication or other management. However a fixation might be more amenable to modification. For example if someone were particularly cruel and made a hurtful comment, it can result in a person carrying that wound for a while. A greater problem might occur for a child who was raised by parents who were critical of appearance and developmentally a poor image was made a deep part of a person's identity.
Both of these situations can improve by applying the cold light of truth. I worked with a guy once whose face was one half a purple birth mark. I observed that while strikingly noticeable at first, after two weeks one never really gave it much thought.
The superficiality of appearance and the opinions of others are more strongly held by younger people. As one gets older, one finds that deeper things have greater importance. Consider the girl that marries a handsome young man only to regret ten years later that she would have been happier if she had married a guy who had a sense of humor.
Another technique to experiment with is that if you have a poor view of your body, stop thinking about is so much. Even though it is negative, it can still be a type of vanity. If you can divert more attention to your work, or other interests, it may allow enough of a distraction to help the negative emphasis to start to fade. If you are somewhat alone or have too much time on your hands, you might consider getting a puppy. They are affectionate no matter how you look and they require so much care, it can fill the time for someone who has too much of it on their hands.