There are two causes of ear problems when scuba diving. The first is the prolonged and frequent presence of water in the ear canal. The second is the effect of the water pressure (barotrauma) on the eardrum (tympanic membrane). Water in the ear canal causes waterlogging, washes away the protective waxy layer on the skin. It also contains bacteria or chlorine which can cause irritation and infection of the external ear; swimmers' ear. The waterlogged skin loses its ability to protect against bacteria. This allows them to colonise the dermis, causing redness, soreness, itching, flaking and discharge. Deafness often comes about due to the accumulation of debris, wax and dirt in the canal.
A good pair of ear plugs will protect the ear from water by keeping it out but should only be used in shallow water. Using ear plugs in deep water can lead to ruptured ear drums. Moulded earplugs are the most effective for this as they are non-porous and fitted to your ear canal. They are even available in antibacterial versions. These will kill the bacteria which commonly cause ear infections.
The second problem, barotrauma, is the result of the pressure of the column of water above your head when you are at depth. The middle ear contains air and the eardrum acts as a barrier between the water and this air space. As you descend the pressure increases. It doubles for every 10 m depth that you go down; you need to equalise the pressure on either side of the tympanic membrane by swallowing. This opens the Eustachian tubes and allows the air pressure in the middle ear to equalise with that of the nasal passages.
If you have a cold or other upper respiratory infection, it may not be possible to equalise the pressure. This is due to inflammation in the area. In this event, as you change depth you may experience a perforated eardrum. This happens when the pressure on one side exceeds that which the eardrum can withstand.
A perforated eardrum is very bad if you are a keen scuba diver because it stops you entering the water until it has healed which may take several weeks. In the event of ear problems from scuba-diving it is very important to seek medical advice as soon as possible. Stay out of the water until a health professional tells you it is safe to return.