The people with this phobia probably wear sweaters and pants throughout all four seasons. They suffer from gymnophobia, the fear of being naked or being seen naked. It can also extend to seeing other people naked. This fear can stem from perceived inferiority, and a detrimental notion of the proper body image.
It can manifest itself into extreme body shame in which people do all they can to conceal their body and even its shape. In some cases, gymnophobia traces back to a past event where a person was exposed in front of several others. Being seen again naked, or slightly exposed, can bring back the shame and embarrassment of that incident.
The phobia can also be linked to a general anxiety about sexuality.