Herbal supplements are used widely, and some of these supplements may stimulate the immune system in ways that could be harmful for people who have or are prone to autoimmune diseases. 
There are a number of herbal medications that have been studied and have immunostimulatory effects.  Among these are Echinacea, the algae Spirulina platensis and Aphanizomenon flos-aquae.  We recently reported three patients with autoimmune disease, two of whom had pemphigus vulgaris, whose disease exacerbated shortly after beginning one of these herbal medications (Lee and Werth, Arch Dermatol 140:723, 2004).  In one case of dermatomyositis, the patient re-flared several months later after rechallenging herself with the same herbal product. 

These herbs seem to affect the immune system by increasing pro-inflammatory proteins produced by inflammatory cells, and their effects have been studied in a number of experimental models.  Studying the potential mechanisms and effects of these herbs in humans has been done in only a few studies, and much more work will be needed in order to document their potential toxicity in patients with autoimmune diseases.  Until these studies are performed, it would be prudent for patients with pemphigus vulgaris to avoid potentially immunostimulatory herbal medications.