In the worst reaction, the customer collapsed outside the café and went into anaphylactic shock before being treated at the hospital's emergency department.
A recent Ashburton District Council report highlighted the seriousness of two recent incidents.
Miscommunication resulted in customers receiving food they were allergic too, the report said. The cafés were not named.
In the first incident, a café guest with a history of severe allergies ordered a vegan bagel and notified café staff of their condition.
The person was given a gluten-free bagel instead and suffered a severe allergic reaction.
They alerted staff, left the premises and collapsed and require treatment at A&E for anaphylactic shock.
The investigation found a communication breakdown was to blame where staff failed to record and communicate the correct allergies to the food server and cashier.
In response, staff retrained on allergies and procedures were improved to communicate between workers when a customer alerts them of their specific allergies.
In the second incident, a guest with a nut allergy visited a different café.
The person ordered a dessert item advertised as having a chocolate sauce topping. But it was actually a Nutella sauce topping, causing the customer to have a severe allergic reaction, which also required treatment at A&E.
The investigation found that the purchased item was new to the menu and incorrectly listed as having a chocolate topping.
Since the incident, that café has corrected its advertising labelling to reflect the use of Nutella. They have also improved the checks on food when being sold, with staff retrained on allergies.
Ashburton council's compliance and development group manager Ian Hyde said the two cafés concerned had been audited in the reporting period before the incidents and were found to be operating satisfactorily.
"How often an operation gets checked will depend on whether it is a high or low-risk business,'' Hyde said.
"It will also depend on how well food safety is managed. Those who are doing well will be checked less frequently."
The monitoring of the district's food services was contracted out.
By Jonathan Leask, Local Democracy Reporter
■ LDR is local body journalism co-funded by RNZ and NZ On Air.
