When you come into your home you carry in all sorts of things that are present in outdoor air, including pollens, fungus, bacteria, cigarette smoke, car exhaust, mildew and fertilizer, just to name a few. They come in on your body, your hair, your skin and your clothes. No vacuum can significantly reduce the number of mites or other allergens in your carpet, even with short pile carpeting.
Powdered cleaners are better at removing allergens while cleaning.
Steam cleaning adds moisture to the mite environment, contributing to mite growth. If you are the allergic person in your house, and you are also the housekeeper, it's better to seek professional help. Using a nasal spray can be extremely effective in reducing allergy symptoms. Allergy practices can sell you a reusable spray bottle kit designed for nasal lavage for a very reasonable cost. Use it as often as needed to reduce stuffiness.