While hot water is good both for comfort and hygiene, this is definitely a case where too much of a good thing can be bad. You might have had water too hot for your hands at a time or another, but that’s not what we’re talking about. If you were to have water coming at a temperature of 160 degrees, which is what most water heaters can put out, you can have scalding within a few seconds. If this were to happen to an older person or a young child, they might need medical attention.
To avoid water from your faucet coming out at those high temperatures, you need to have an anti-scald valve installed. These devices are made to mix the incoming hot and cold water to achieve a stable, comfortable temperature.
They also serve a second purpose by preventing temperature fluctuations from water running to other faucets, toilets or showers.