If you put the affected area under the hottest water you can, you cause the nerves to effectively burn out, overloading the signal to prevent the itch from triggering.
Especially for poison ivy it worked wonders when you have a bad rash, although you shouldn't put hot water on (opening the skin pores) if there's any chance you still have the oil on you, as it'll just get deeper in. This is for the days after once you're suffering.
Being a Brit and moving to the US I had no idea what poison ivy is, and learned the hard way. Standing under the hot shower and burning the ivy itch away causing a feeling that's basically pure ecstasy. It's an incredible feeling of relief, coupled with every nerve going nuts.
Could also be something specific to mosquito bites, I've read the denaturing argument too. My brother in law swears by holding a lit cigarette tip just above the bite to have a similar effect. It never worked particularly well for me, but bathing area with hot water always works for a bit.
The link actually links to the actual "science" page - https://just-heat-it.co.uk/pages/study which is page on a study of the effect.
> The treatment of insect bites using heat-based devices such as heat it® leads to significant itch and pain relief. This is proven by the world's most comprehensive study on the effectiveness of thermal insect bite healers.
> "Efficacy of Concentrated Heat for Treatment of Insect Bites: Results of a real-world study" - Metz M et al. | Published June 26, 2023 in Acta Dermato-Venereologica by the Society for Publication of Acta Dermato-Venereologica.
The paper itself is here: https://medicaljournalssweden.se/actadv/article/view/11592/1...
Conclusion:
> This study shows that concentrated heat induced by a heating device reduced pruritus caused by insect bites and stings, even if the insect bites occurred more than 6 h previously. Across more than 12,000 treatments registered, less than 1% of participants reported side-effects. Further investigation of these side-effects showed that none posed a serious risk to the participant.
But, it doesn't go into the possible reasons why.