Will consuming onions help to reduce your body temperature, or prevent heatstroke? Some common variations of this claim include applying onion juice to your skin, or even just carrying an onion in your pocket, hat, or even a bag (yes, that is commonly suggested). It seems to most commonly be touted as a prevention - or even a treatment - for heatstroke.
Suggested explanations for this "cooling" effect range from "the onion absorbs heat", to the antioxidants or antihistamines in the onion cause the effect. I can't find anything about why people think a detached onion in a bag or pocket will help with the heat, though.
This may be a regional belief specific to India, as I've only ever heard this from coworkers who grew up in India, and it is most prominently touted in India-related websites.
For example, the Indian company INLIFE Group suggests in a 2014 article:
Onion is a great friend in the summer. It has good heat absorbing property. Keeping one white onion in your pocket or purse will help you avoid sunstroke. Applying thick onion paste on the affected person’s forehead is also an effective sunstroke treatment.
Another example is the Times of India lists onion juice as one of 7 effective home remedies to prevent heat stroke; or the New Delhi Television website, which also lists Onion Juice as one of 10 natural home remedies to treat heat stroke:
This is one of the best remedies for treating a heat stroke. Lot of Ayurvedic practitioners suggest that this should be the first thing that you must reach out for. Applying onion juice behind the ears and on your chest can help bring down your body temperature. For therapeutic purposes onion juice is more desirable, but you can roast some raw onions with cumin and honey and have it. Raw onions in chutneys or salads can also cool your system.
Edit: My main question is about whether consuming onions helps with cooling the body, but I've included the "carrying an onion" for context, as consumption and carrying are often suggested together.
Edit 2: I should also mention that a quick pubmed and Google scholar search for onions and heatstroke don't return any relevant results.