Vinegar and lemon can both help neutralise any bad smells. Of course, vinegar has a pretty intense smell itself, but once it starts to evaporate, it often neutralises any unwelcome smells, such as fish, onion or smoke. Placing a bowl of vinegar in a room or using vinegar while cleaning can help reduce any smells. Lemon has a refreshing smell, and the natural acids it contains are able to absorb and neutralise any odours. Squeezing out half a lemon in a room is a great way to spread a fresh smell.