Minoxidil 5% gives me acne. How can I avoid this side effect or reduce it?

The liquid formulation of minoxidil tends to cause acne for some people due to a preservative ingredient that is not found in the foam. You may want to try switching to minoxidil foam. Another option is low-dose oral minoxidil. This is a nice option for patients who have difficulty with topical application. The oral medication is not FDA-approved for this indication so it is prescribed off-label to treat hair thinning. I recommend a consultation with a hair specialist to further discuss these options.

Like all liquid medications, the minoxidil is with a "carrier." Many people are actually allergic to one of these materials vs the other. For minoxidil, I have more patients are allergic to the carrier in the liquid than the foam. The next step is to switch to the other one. Most likely, the issue will go away. 

This may be an allergic reaction.  Reactions to minoxidil are usually caused by what it's dissolved in, not the minoxidil itself.  You could try switching to foam, or try a different brand.

If you are using the minoxidil foam, switch to the liquid and if you are using the liquid switch to the foam. You may be allergic to the carrier in the minoxidil