Another possibility:

My skin is acne-prone, on my face and chest. I have to be careful about the moisturizers that I use. Though I've never gotten pimples on my scalp (lol), it is very possible that my scalp didn't respond well to comedogenic ingredients. I'm pretty positive that at least some of the ingredients in my co-wash were comedogenic. I'm pretty sure this would rule out cowashing for me in general. And again I hope I didn't do any irreparable damage to the follicles.
Originally Posted by PomegranateCurl
Potential bingo: acne is actually as much inflammatory condition as it is an infective one. You definitely should be checking ingredients and again review your diet - plenty can be done to balance hormones, moderate the immune response and reduce systemic inflammation.

No, acne does not necessarily preclude co-washing with any product for anyone with acne, plenty of people successfully use the Oil Cleansing Method, but using a decent emulsifier and not over stimulating works best. I definitely would not choose products which are highly moisturising or contain lots of plant extracts, simple and gentle, acidic pH and rinses clean.

Comedogenicity is far from the only issue, known irritants and ingredients that damage the skin barrier/ acid mantle (keeps bacteria out) are just as much of a risk. Some with acne respond really well to dropping sulphates and other anionic surfactants, some worsen before they improve as the skin flora recovers and the skin becomes better hydrated.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect