I was wondering whether an Allergen warning feature is feasible. The idea is that the app would warn you if you scan the barcode of a product (or choose a food entry within the app) that contains (or is likely to contain) something you're allergic to.
A feature like this could also leverage the power of the community, where they can put a thumbs up or down for foods that are unsuitable or if they've had a bad experience in the past after consuming it (e.g. coeliacs or those with lactose-intolerance). This feature could also translate well for users who opt not to eat specific foods (e.g. vegans/vegetarians). It can be surprisingly easy to miss things on food labels, especially when the font is small on the packaging.
On registration, a user specifies that they have a gluten/wheat allergy. They buy a newly-stocked product from the supermarket that is sold in the "free-from" or "gluten-friendly" aisle.
Whilst preparing to cook it, they scan the barcode and the entry for the food appears, paired with a "community allergen rating" of 75% (indicating that others with a similar aversion to gluten find it somewhat safe to eat).
Shortly after the meal, the user starts to feel unwell and realizes that the product was produced in a factory that also handles wheat, dairy etc. Clearly it is unsuitable for them to consume in future, so the user selects the food entry in the diary and gives it a thumbs-down. Other users have a similar experience and give it a thumbs down too.
A few months later, a user with a similar allergy signs up for Cronometer and buys this product. On scanning it, the "community allergen rating" is now 15% and the app warns them that it may be unsuitable for them to eat (and prompts them to double-check the packaging). The users re-checks the packaging, avoids eating it and obtains a refund or gives it away to a food bank.