Any situations where there is the chance of liquid or chemical splashing or when there is significant risk of material or debris that may be directed at the eyes then goggles are highly recommended. Since they do make a full enclosure over the eye area they prevent contact with these types of foreign materials and the eye in a much more complete fashion than safety glasses. Glasses, even those with side shields, leave areas to the outside corners and edges of the eye at risk for chemical contamination or exposure to object and debris. This can include both small and larger objects, both with are capable of causing serious eye injury. Goggles are also critical in situations where safety equipment needs to worn over top of prescription glasses. Wearing safety glasses in these situations is typically not practical unless you have prescription safety glasses that allow both protection and vision. Do I need to buy different sizes of lab safety goggles? Goggles are designed to be adjustable to any head or face size. They adjust by simply pulling tight on medium sized elastic strap that attaches to each side of the frame of the glasses just behind the temple. This allows anyone to wear the goggles, even over other prescription or protective eyewear. Individuals with very narrow or small faces may find that a children's goggle is a better fit, but this is uncommon for most adults. What if I have prescription glasses, can I get prescription goggles? Prescription goggles are not an option, but the very design of the goggle makes it easy to wear with your glasses. The goggles are very deep, sitting well out from the face, meaning that glasses can easily be worn underneath. The goggles will not press or rub against the glasses either on the frames, lens or the bridge of the nose, ensuring that the combination is comfortable even for long periods of time. For additional safety you may need to consider prescription leaded safety glasses underneath the goggles in highly specialized laboratories or medical work situations. Again this combination will provide the maximum protection for your eyes with two very lightweight eyewear options. Why are lab safety goggles ventilated, doesn't that pose a risk? Lab safety goggles are ventilated with very small holes on the sides of the glasses which corresponds to the area of the face just over and behind the temples. This allows for the release of humidity and heat under the glasses, helping to prevent any type of fogging with normal wear. Since the ventilation is indirect on and the curved parts of the sides of the glasses the risk of any transfer or contact with any splashed chemicals or materials is almost nil. These goggles have to meet all required safety standards including ANSI, CE and UL standards, just be sure to check the information that all standards are met and you can wear the goggles with confidence