The ears are one area where pressure can feel much more intense. Small amounts of air get trapped within the ears when entering the water. While the water does get into the canal, the eardrum is effectively impenetrable so it leaves air behind it. Think of the eardrum as an orchestra drum and how the air behind that will squeeze when you hit it. The same happens behind the ear drum and that pressure increases as the volume decreases. There is simply nowhere for the air to go.
Boyle’s Law, a physics principle, is active here and is something taught in all the initial scuba courses. Just jump in the water and you’ll go back to those elementary science lessons!
According to Boyle’s Law PV = constant (at a given temperature).
Look scary? Well, the truth is that it’s simple. You simply have to measure the volume (V) and pressure (P) and multiple them. It remains constant because when one goes up the other goes down. Let’s use a balloon analogy. When you squeeze it the volume inside the balloon decreases but the pressure increases and when you let go it returns back to the initial state. When the volume is halved, the pressure is instantly doubled.
Now moving back to the eardrum, when the volume behind it is lowered, the pressure will increase. Eventually, this causes discomfort and can lead to ear damage. But it is possible to deal with that and that’s relatively simple too!
As you descend into the water, you will feel the pressure building inside your ear. Just hold/pinch your nose and blow against it gently or simple swallow. The air will move out of your ear canal and into other parts of the body with more volume. The change in volume will lead to less pressure in your eardrum but very little in the other areas as the change isn’t noticed as much. The air system within the body is connected throughout.
Keep doing this as you descend further. For every 10m/33 feet, the water pressure increases by one atmosphere (atm). The air that is trapped is continually squeezed but as the pressure inside and out is equalized, there is no longer the discomfort.
There are numerous factors when it comes to the pressure severity.
Colds/sinus problems can stop the air moving around the body properly. Avoid diving when this happens. Allergies lead to sinus issues and while medicines can help, they can cause drowsiness, which leads to your mental focus being compromised. This is dangerous for diving.
Perform the equalizing tip throughout the descent and ascent, even if you don’t feel the need to. Avoid doing it when you get the uncomfortable feeling.
Air can also be trapped in your face mask and other areas. Your face mask will have the same pressure while descending. The glass plate is durable and will work well against the pressure but the rubber part, the skirt, can cause some problems and lead to pressure around your eyes.
Invest in a good mask and make some exhalations through the nose when needed. Do this slowly to avoid the mask fogging.
Your regulator will take care of much of the equalizing naturally in other cavities with air, including the lungs.
Enjoy your dive the whole time by equalizing regularly and safely.