Why water doesn't help against chillies

If you've ever had a chilli before you're probably quite familiar with the not entirely pleasant feeling of having your tongue lit on fire. On more than one occasion, having been a bit too flamboyant with tabasco bottle I almost thought I could breath fire.

Now you're mom, or someone else, will probably have told you to drink milk. Water doesn't help they say, and I have no doubt you've experience it for yourself. There's actually a very logical chemical explanation behind this.

"labeled for reuse" https://pixabay.com/p-1053657/?no_redirect 

Now substances can be classified as one of two things. Either polar, or non-polar. This essentially states whether or not there is a greater electron density in one area of the molecule versus another. To determine whether or not a molecule is polar you first look at the bonds. If two substituent atoms are different molecules, they will have a polar bond. The amount of polarization will depend on their respective electronegativities (the pull of a nucleus on a shared pair of electrons), the greater the difference in electronegativtiy the more polar the bond. But just having polar bonds doesn't necessarily mean that a molecule is polar, to determine this you need to look at the symmetry of the molecule. If it is symmetrical, i.e. the shape of it as well as the substituent atoms attached, the molecule is said to be polar. If this isn't the case, it is a non-polar molecule.

Now when such substances are dissolved in solution, there is a helpful phrase that helps characterize their properties: "like dissolves like". In other words, a polar molecule will be dissolved by a polar solvent, and a non-polar molecule will be dissolved in a non-polar solvent.

Capsaicin, the molecule largely responsible for "spicyness" is a non-polar molecule. Water, on the other hand, with highly polarized bonds and two lone pairs (making it non-symmetrical), is highly polar. Thus drinking water doesn't really do much. In contrast, milk contains some amounts of fat, i.e. triglycerides, which are long chains of saturated hydrocarbons. These fat molecules are non-polar, allowing the capsaicin to dissolve into the milk and thus is removed from the mouth. And voila, your mouth no longer feels like a dragon breathed into it.

By the way, ice cream does the same trick.