I don't know of any spells off-hand, but i think it would be a fun project to create one.
If i were doing such, i might make a doll baby out of Sculpey or clay to represent the target, complete with red acne bumps. I'd also cut out some of those before photos you see in acne ads like Proactive and incorporate them into the working as well. Of course when you call down the curse, you'd use language and visualizations towards your goal.
Like in my thread, I do beleave that you can give a disease or sickness like acne as well as remove it. I just havent gotten any proof of it yet. I think its a cure like any other, weather you brought it on yourself or another person or diety did. Let me know what you find out.
Curse's tend to attach themselves to the person's weakest body system, unless they are programmed otherwise.
If someone is clumsy, a curse can manifest as an "accident." If someone has hypertension, a curse can manifest as a heart condition. If someone has poor skin, a curse can manifest naturally as acne or some other skin malady.
why do you want to give acne to someone? For me it is better to have more effort on defensive magic. like when somebody voodoos on me but the voodoo does not work because I am already protected by another magic so nobody gets hurt.
I am not surprised why some witches keep their ''offensive magics'' secret and would prefer to be called silly for not proving their abilities. if they revealed/showed them, many people would attempt to get them and potentially abuse them.
just my opinion....
I myself learn offensive magic but so far I've never abused it (I am not even sure I can use it) the reason why I learn magic is beside I like it I just wanna protect myself.