May be an optional extra for your model
Cooker hoods are designed to extract and vent outside the property. If inside recirculation will be used when installing then charcoal filters will need to be fitted to purify the air from bad smells. Charcoal filters are sometimes an optional extra which you may need to purchase. Should you require filters you can purchase them via the spares section of this website.
Check the product specifications of your hood to see if they are included.