Adding benzyl benzoate (0.03%) and eucalyptus oil (0.2%) to the wash cycle kills mites. Plus from another research team, the answer comes in essential oils alone added to the wash. Natural oils such as eucalyptus oil, or tea tree oil, have been found effective in killing mites, however, eucalyptus proved to be the best. How does it work? Doctors are not sure, but one theory is that the solution breaks down lipids in the mites body causing death. This may not kill all mites but if you need to warm wash it's a method worth using. There is another thing to keep in mind if you wish to use this method of mite control. Best to soak the wash in the solution for 30 minutes before beginning the cycle. The concentration of water to oil is 1 to 120 (approximately 0.8%). Please note that the scent of eucalyptus oil may linger for 2 to 3 days.
'The effectiveness of benzyl benzoate and some essential oils as laundry additives for killing house dust mites.' Lindy McDonald, Euan Tovey, J Allergy & Clin. Immunol. Nov. 1993: p771-772
'Mite control with low temperature washing. II: Elimination of living mites on clothing.' Bischoff ERC, Fischer A, Liebenberg B, Kniest FM, Clin Exp. Allergy, 1998; 28:60-65
'A simple washing procedure with eucalyptus oil for controlling house dust mites and their allergens in clothing and bedding.' Tovey ER, McDonald LG, J. Allergy and Clin. Immunol. 1997; 100: 464-466