So looks like one broad conclusion is: the memory foam type of ear bud tip is normally toxic, so go for medical grade silicone replacements. There are options

So looks like one broad conclusion is: the memory foam type of ear bud tip is normally toxic, so go for medical grade silicone replacements. There are options available on major e-commerce sites. The ones I choose have a stainless steel nozzle and are supposed to enhance the sound reproduction.