Asthma-related hospital visits have skyrocketed 200 per cent in the past week as students head back to school.

NSW hospital figures show a sharp rise in young people attending emergency departments for respiratory problems in line with the annual national asthma "spike".

Experts say the changeable weather and the spreading of bugs at the beginning of the school year could be to blame for the surge.

"Statistics from the past decade show that this phenomenon happens in February and March every year," said Asthma Foundation NSW chief executive Greg Smith.

"This year's figures haven't yet topped last year's peak, but it is still one of the highest in recent years."

Mr Smith said the changeable weather could be a factor, as people with asthma were very sensitive to fluctuations in temperature.

"Stress, the change of environment as children start or move schools, the cocktail of germs, cold and flu viruses that children can pick up once they come together en masse can all trigger a potentially fatal asthma-related illness," he said.

One million school days are lost each year to asthma.

Asthma Foundation NSW is writing to the department's of health and education asking for collaborative state and federal support in rolling out a prevention program aimed at stopping perennial asthma spikes.

"We know our health system is already under severe strain and we believe that by getting the message through to parents and schools about good preparation and management that we could help save valuable health resources," Mr Smith said.

The foundation urges parents to ensure asthmatic children have an asthma action plan that is reviewed annually.