Researchers have added a new dimension to the world of virtual reality - smell. 

A small, wearable virtual reality (VR) interface that allows users to smell several different odours - including rosemary, mojito, pancake, and durian - has been unveiled in a Nature Communications paper. 

The devices can quickly and accurately generate odours in a localised area and connect wirelessly to VR worlds for an immersive and more realistic user experience. 

Future research could allow users to detect smells when playing video games, 4D films, and in virtual teaching environments, the authors suggest.

Human-machine interface systems have previously been developed to simulate vision, sound, and touch in VR, but designing a system for smell has been challenging. 

Current smell interface designs have bulky formats using bottles of liquid perfume or wired, rigid VR headsets that limit their practicality. 

Wearable odour generators that are lightweight, flexible, wireless, and equipped with a wide selection of odour types and programmable scent intensities have yet to be created.

Researchers at the City University of Hong Kong designed two wearable formats of the wireless smelling interface. 

Using millimetre-scale odour generators, the first format is directly attached to the skin under the nose with two odour options, and the second is a soft mask capable of generating nine different odours. 

The authors demonstrate its customisability with a selection of 30 different odour types — including pineapple, ginger, green tea, caramel, and candy. 

The tiny odour generators contain scented paraffin wax, which can be heated to release specific odours quickly (in as little as 1.44 seconds) and accurately in a localised area.

The authors suggest several applications for the research, such as for delivering scent messages as an alternative communication method, triggering emotional memories, and enhancing user interaction in VR worlds.