If you have an allergic reaction to polyester, the clothes you wear, the linens on your bed and the upholstered pillows on your couch could cause an itchy rash. Although polyester allergies to fabrics are unusual -- toys with polyester hair or fur are more typical allergens -- they do happen.

A variety of conditions, from viral illnesses to allergic reactions, can cause red bumps to appear on the trunk of your body. Although in most cases red bumps on your trunk are mild and treatable, you shouldn’t use any medications on the bumps until you know what caused them.

There are many diseases that cause skin rash. According to MedlinePlus, rashes affect the color or texture in a person's skin. The cause of a rash can often be determined based on the observable characteristics of the rash and other accompanying symptoms.