Rotorua's rotten-egg sulphur pong might be hard on the nostrils, but an international study has dispelled fears that it slows the brain.

Exposure to hydrogen sulphide gas has been linked to a range of negative effects on the brain, but inconclusively.

To investigate the theory, US and Kiwi scientists looked to Rotorua - the largest population in the world exposed to such long-term low levels of hydrogen sulphide gas (H2S).

The researchers surveyed more than 1600 residents between the ages of 18 and 65, gauging their exposure to H2S at work and at home, and over previous decades.


A round of tests were also carried out, measuring their mood, visual and verbal episodic memory, attention, fine motor skills and psychomotor speed.

When compared, the scientists found no link.

"The key thing is that we have no evidence of a harmful effect," said co-author Professor Michael Bates, of the University of California at Berkeley.

The findings, published in the journal Neurotoxicology and Teratology, come as part of a wider study on potential health effects of Rotorua's hydrogen sulphide.

Last year, the researchers published a study finding the the gas had no negative impacts on people suffering from asthma.

Further research is expected to be released.