I have purchased some outdoor clothing made of 83% merino wool. The manufacturer states in their care instructions to "use regular detergents, not wool detergents". What is the reason for them recommending this? I thought wool was supposed to be washed using wool detergent.
The folks at Smartwool explain why you should not use fabric softener on Merino wool:
Machine-wash on gentle cycle in warm or cool water (avoid hot water as heat may shrink wool). Use mild soap, no bleach or fabric softener (bleach destroys the Merino wool fibers, and fabric softener coats those fibers—reducing their ability to naturally manage moisture and regulate body temperature).
And at Icebreaker:
Use a normal warm or cool machine wash cycle with regular powder or liquid detergent. Separate light and darks as usual. Don’t use softeners or bleach. ... Using softeners will coat the merino fibers and reduce their natural ability to breathe and regulate moisture and temperature.
Wash the garment in a normal wash cycle between 30°C and 40°C using regular powder or liquid detergent. For merino wool, you don’t need wool detergent. This is intended for conventional wool and can thus damage you merino wool! Don’t use bleach or fabric softener, either!
We recommend using gentle or wool-specific detergents. Be sure to check that your detergent is free of any bleaches or fabric softeners.
Presumably, there are some regular wool detergents that contain softeners, and are to be avoided.