Normally, smoking is a big 'no-no' when it comes to skin care. It give you crow's feet and it can cause a weird tint, sort of gray looking, to your skin. But, I said, that's normally. Nothing is normal about marijuana, which seems to be a drug assigned to any number of new treatments on a daily basis. The latest one associated with ganja is believed to clear up by allergic dermatitis according to a study done in Switzerland (I guess that's one of the few countries that could conduct a study like this), Study: Substance in Marijuana Clears Facial Dermatitis:

A substance found in the cannabis plant helps the body's natural protective system clear dry, scaly skin rashes caused by allergic dermatitis, according to researchers from the U.S., Germany, Israel, Italy and Switzerland.

Allergic dermatitis commonly causes acne-like rashes on the cheeks, eyelids and neck, as well as on areas of the elbow and the back of knees. Prolonged episodes can lead to facial wrinkles, thickening of the skin and facial pigmentation. The problem begins in youth and can continue through adulthood.

Allergic contact dermatitis affects about 5 percent of men and 11 percent of women in industrialized countries, according to an article published in the journal Science.

A group of domestic and international researchers have found that two naturally occurring cannabinoid (cannabis-like) components found in the body's endocannabinoid system - one from the brain, named anandamide and another from the intestines named 2-AG provides protection against dermatitis.

These cannabinoids have similar effects to those of the active components in hashish and marijuana, produced from the cannabis plant. Further research using mice has shown that THC - the ingredient in marijuana that produces a "high" in users - significantly decreased the allergic reaction in comparison to untreated mice.