Sounds like you may be suffering from tinia versicolor, also called pityriasis versicolor. This is caused by an overgrowth of a fungus that is found naturally on our skin. It can be caused by antibiotics or birth control pills and causes either light brown splotches or pale patches that are lighter than the natural skin color. An easy home remedy is dandruff shampoo. You should use the shampoo on the affected area daily for about a week. It can take several months for the skin to return to its natural color. If it continues to spread after one week of the shampoo treatment, you may need to see a doctor to get a stronger, prescription treatment.