I am not sure about the washing detergent, I have tried many but still end up coming back to Persil or Ariel. You note that you are trying to fight a BO problem on your sons clothes, this might seem odd but have you tried White Vinegar, you spray the armpit area, leave for ten minutes and wash as normal, you can also use it in place of Fabric Conditioner, not only is it cheaper but your towels will thank you as they come out super soft and it helps to keep your machine clean, works for me and you have nothing to loose....... assuming you have not tried this already.