Mites live in the padding, not on top
Dust mites are microscopic arachnids, related to spiders, that feed on shed skin cells. A mattress provides everything they need: warmth, moisture, and a steady supply of organic material. They do not sit on the fabric surface. They burrow into the filling, whether that is foam, fibre wadding, or the padding wrapped around a spring unit. Their eggs are deposited deeper still, in the compressed layers where temperature and humidity stay stable. This is why surface observation tells you nothing reliable about a mattress's condition. The mites you cannot see on top are not absent. They are simply somewhere the eye, and most cleaning tools, cannot reach.
A vacuum only lifts the surface fibres
A vacuum cleaner works by suction across the top layer of fabric. It lifts loose particles, surface dust, and anything sitting within the pile of the ticking. It does not pull material out of compressed foam or fibre padding below. Mites living in those layers are simply not in the path of the airflow. Running a powerful vacuum over a mattress will remove surface debris and may pick up some mites that happen to be very near the top, but the colony living in the padding remains untouched. The surface looks cleaner. The conditions inside do not change.
Sunlight and airing do not penetrate deep enough
Placing a mattress in direct sunlight is a traditional remedy, and it does have some effect on the outermost layers. Ultraviolet light can damage organisms on an exposed surface. The problem is that padding insulates. The internal temperature of a mattress in full sun rises, but not uniformly, and the core of a standard mattress stays significantly cooler than the outer face. The same is true of airing: moving air circulates around the outside of the mattress, not through its interior. Mites living in the padding are not exposed to the conditions that are otherwise hostile to them. The outer face changes. The inside does not.
Heat penetrates where surface cleaning cannot
The effective approach is applying heat at depth. Hot-water extraction forces heated water and cleaning agent into the padding under pressure, driving heat into the foam or fibre layers where mites and their eggs are present. At the temperatures this process reaches, mites do not survive. Neither do their eggs. A detergent applied by hand or sprayed onto the fabric surface and wiped away cannot achieve the same result, because it sits at the surface and carries no heat into the inner layers. The mechanism depends on penetration: the heat must reach where the mites are, and the mites are not at the surface.
A humid coastal climate makes moisture management critical
In a coastal environment where humidity is high for much of the year, a mattress holds onto moisture readily. This matters because mites thrive where warmth and humidity combine, and a mattress absorbing ambient moisture provides exactly those conditions throughout its padding. After a cleaning that leaves water behind in the inner layers, the first humid day draws that moisture back to the surface as odour. A proper extraction clean removes the moisture it introduces by pulling it back out during the process. Getting this balance wrong does not address the mites. It makes the conditions inside the mattress better suited to them than before.
