Hi Julia, thanks for your question. Fabric conditioner does not immediately impact the underarm microbiome. We have far more bacteria in the underarms than bacteria on the washed textiles. Nonetheless, our recent research showed that textile laundering has a huge impact on the microbiome, and will lead to more resistant and virulent microbiome. So it may contribute in the long run to a more unwanted situation. The problem however is that it is such a wide-spread habit.. Best, Chris