What does a scientist wear to work? Whatever they want. Just kidding, but not really.
I want you to have a real image of what scientists look like and do on a daily basis. This is different for different kinds of scientists, so I can only speak to my life as a molecular biologist.
First of all, we do not dress like this (though I did dress like that for Halloween one year - I'm the Bio Geek): Typically to work in a lab there are some rules - the rules are to keep you safe but also to keep your experiments free from contamination. In the lab, you often work with caustic chemicals, so closed-toed shoes and long pants are encouraged, if not required. Some labs are more strict and also require long sleeve shirts. When I was in grad school, this was a typical day and typical outfit (and typical messy desk - I think I was writing my thesis at the time).
When doing experiments, you typically wear person protective equipment (also know as PPE). This includes a lab coat, gloves and maybe safety glasses. PPE is generally annoying but necessary. First, PPE protects you from spills. I worked with hydrochloric acid and cancer-causing chemicals all the time so I didn't want them to be touching my skin. Second, PPE protects your hands and eyes from these chemicals. Third, it limits your skin cells, bacteria on your hands, or anything else from getting into your experiments. When working with DNA, you don't want your DNA to get into your experiment and mess up the results, and when working with cells you don't want random bacteria from your hands to contaminate your cell cultures. There are other labs that are much more strict because they have more dangerous agents in the lab, so you may need a ventilator or a suit with negative pressure.
Scientists don't spend all of their time in the lab. Meetings, where you present your research either as a talk to an audience or on a poster that people walk around to see, are common. For those, I typically dress up, because even as a scientist, making a professional impression is important. This is my first ever poster presentation when I was an undergraduate presenting at the Beckman Symposium in California.
These days I don't work in the lab anymore, so I dress business casual nearly every day. Again, to make a good impression and look professional, however I know researchers who have their own labs that wear shorts and sandals to work every day. Once when I was at a meeting in D.C., a researcher from the West Coast made a big deal about how he wears a tie on the East Coast but doesn't on the West Coast. Either way, most scientists are just normal people who dress like everyone else, but sometimes need to protect themselves and their science with PPE.
Dr. Cathy Seiler is the Program Manager for the tissue biorepository at St. Joseph's Hospital and Barrow Neurological Institute. She has her BA in Biochemistry and Molecular Biology from Boston University and PhD in the Biological Sciences from Cold Spring Harbor Laboratory. Her research and teaching focuses on genetics, cancer, and personalized medicine. Find her on Facebook at www.facebook.com/thingsitellmymom