Cell culture contamination sources can be the tools that you are using for culture itself

Some known/unknown contaminants must be lingering around your laminar hood, while you are working on your routine cells. You must be aware of viruses, bacteria, fungi, mycoplasma, endotoxins, etc. however, you should also understand that your surrounding can also be a major source of contamination, like chemicals that you are using, glass beakers, plastic products that you are using while culturing.