This may be a simple case of a teen who hasn't yet realized the necessity of "deodorize before you socialize," but it's important to confirm that there isn't anything under the surface that needs more than some teaching and some deodorant...
My LPN class was made up of equal parts of federally employed NA's, single parents receiving AFDC, and "general admission"students from the community. One of my classmates was a single mother of 4 children, living up in the hilltowns somewhere. She did not have a car, but the Dept. of Public Welfare did provide transportation to and from classes and clinicals. At some point during the winter, several of us noticed that her uniforms were clearly unwashed, her stockings were full of holes, and her hair was visibly greasy and unkempt. Worst of all was her body odor. She seemed to be aware of it, and she kept toiletries in her locker and tried to clean up as best as she could during breaks and lunch.
One morning, she was called out of class and never returned. Apparently, she had had a minor house fire several weeks before, and while most of the home was still intact, she lost electricity and phone services. Without electricity, her well didn't work, so she had been getting drinking water from neighbors and melting snow to for water for flushing the toilet. Her sole source of heat was a wood stove, and they were using candles and kerosene lanterns for light. Somehow, someone discovered the family's living conditions, and had reported them to DCF.
We felt horrible. None of us had considered asking her about how things were going at home. When her hygiene started slipping, no one mentioned it to her, although we rolled our eyes and made faces behind her back. We never thought that offering to help her with such a (relatively) minor problem may have benefited her entire family. This is one of the top five "missed opportunities" I've experienced, and I will remember and learn from it for the rest of my life.