We see them as twins – two people who look the same, who were born at the same time and who shared the same womb for nine months. But as they often "view" themselves singularly, twins may not realize any differences in their appearance until they see a photo of both twins or look in the mirror at the same time. However, sometimes the differences are brought to everyone's attention, making one twin feel inferior, unattractive or ugly in comparison to the other.

According to Dr. Darrick E. Antell, a plastic surgeon who specializes in twin procedures from New York, N.Y., there are many causes, reasons or explanations as to why twins may look different. The most common include the following:

Medications or Medical Treatments – One twin may develop an illness or condition that may require medication. Many medications or treatments can have side effects such as skin changes or weight gain. If the twin is required to stay on this medication or treatment for any length of time, causing a significant change or weight gain, it can cause him to look different than his twin.

Environmental Influences – While twins often look alike, they may not necessary act alike. And these differences in behavior can cause a difference in appearance. For example, if one twin is more active than the other, spends more time in the sun or perhaps swims regularly, they can have changes in their appearance evident in their muscle build, skin or hair color or skin and hair texture.

Illness or Accidents – Quite often, the reason for the major difference in the appearance of twins is due to an illness or an accident. Illnesses such as thyroid problems, diabetes or cancer can change a person's outward appearance dramatically. In addition, bodily injury and/or burns can alter appearance.

Being the "pretty one" is not necessary a good thing. In fact, the feelings that often accompany being known as the more attractive of a set of twins can counteract any benefit that beauty could ever bring. "Oftentimes the 'prettier' twin feels guilty," says Dr. Antell. "The more attractive twin may feel guilty that they were given something their twin was not. Also, as twins have been known to be able to feel what each other is feeling, it is not uncommon for the 'prettier' twin to feel just as unattractive as his/her co-twin, if for no other reason but for sympathy."

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