Firstly, there is a distinction between dust mites themselves, and dust mite allergen, both in terms of how to remove them, and in terms of how allergenic they are. People are generally not allergic to dust mites themselves; they are allergic to the waste and other materials the dust mites produce.
To remove dust mites, washing in high temperatures is best. For example, when ASTHMA AND ALLERGY FOUNDATION OF AMERICA and ALLERGY STANDARDS LTD test washing machines and dryers for asthma & allergy friendly® certification, they test that they can reach and maintain temperatures of at least 55 degrees Celsius for a period of time. This is to kill dust mites.
However, when they are looking at bedding, their approach is not to look at killing dust mites: you use a washing machine or dryer to do that, so it’s included in those standards for machines that are certified. Instead they are looking at whether the bedding item acts as a host and reservoir to the allergen. If you are someone with allergies, you should be washing your bedding regularly, and it should be possible to remove the allergen from the bedding when you wash it. This is also because there can be other allergen present, like cat dander or even pollen that has been transferred from clothes or hair. So the Pure Zees Baby Cot mattress has you covered in any concerns you may have in this regard.
Any bedding that is certified has been tested to show that after seeding the bedding with dust mite allergen, and washing at 40 degrees Celsius, that at least 90% of the allergen is removed. They use 40 degrees because this is part of an international industry standardised test for washing items (ISO 6330). They also use 40 degrees because they are always trying to model the way in which the consumer will interact with their certified products. While many items say on textile labels that they should be washed at high temperatures, many households use the same standard wash cycle to wash everything. If it is possible to remove 90% of allergen at 40 degrees, then at the very least it will be possible to remove that amount also at 60 degrees, or an even higher amount.
However, washing at a higher temperature can also have the side-effect of increasing the wear over time on the product. Another test they do on all of their certified bedding is a repeat wash test – to make sure that if someone washes their bedding item regularly, it is of sufficient quality to withstand this cleaning. They don’t want to see consumers reducing the regular washing of items, because with higher temperature cleaning the product is getting worn out or shrinking.