Dust mites, pet dander and pollen tracked in from outside all settle into carpet fibres over time, and for allergy sufferers this can mean a home that feels clean but is still actively contributing to symptoms, particularly in bedrooms where people spend the most time.
Hot water extraction is effective here because the high temperature itself helps neutralise dust mites and their waste, alongside physically extracting the material rather than just disturbing it the way vacuuming alone tends to do.
For households managing allergies specifically, cleaning every 6 months rather than the standard 12 to 18 month cycle is worth considering, along with mentioning any sensitivities to the crew so they can select a suitably low-residue product for the job.
