Many people find the smell of plastic from a 3D printer to be particularly noxious, but there hasn't been that much research on the long or short term health effects of exposure to 3D printer fumes. Because the differing nature of the particles and compounds put into the air by different filaments, there's no standard way of filtering everything, especially since the smallest particles can't be caught by even the best HEPA filter.
If you only print occasionally the risk is low, but if you are going to be printing a lot (and especially for multiple printers), what the CDC recommends is to vent the 3D printer gasses to the outside, such as with one of our vents paired with a standard dryer hose. They can also hook to any DIY enclosure by simply creating the right size hole.
Here's an example setup with the CR-10/Taz6 vent kit. For this you'd need to order a hose, clamps, and dryer window vent from your hardware store.
The Prusa/Ender setup is a bit more complicated since window inserts are all 4", while the hose we recommend is 3". This setup adds an 3"->4" hose adapter, and the 3" hose is small and doesn't overwhelm the small enclosure. Note that with this setup you need 2 3" clamps and 1 4" clamp.
Every enclosure comes pre-drilled with the vent and mounting holes, but this kit adds the following:
To complete venting to the outside you can find flexible 4" dryer duct hoses or flexible 3" hoses online or at most hardware stores. This can be connected to the outside using the same techniques you'd use for a clothes dryer, or you can purchase one of the many compatible window-venting kits. These items are not included and must be purchased separately. We don't bother to stock them since they're readily available at local hardware stores.
The fan can either be plugged into a USB power supply (not included) or the wires stripped and connected directly into some models of 3D printer.