Many of these therapies are considered "natural" and therefore harmless. However, because of the poor regulations that exist in monitoring these drugs, adverse reactions do occur. Herbal therapy, therefore, should be avoided in pregnancy, infants and children because of the uncertainty of adverse reactions that could occur. There is little incentive for pharmaceutical companies to investigate or standardize these preparations because it is unlikely patents would be applicable.
Because of the assumed safety of natural products, many patients believe these products have "fewer" side-effects. Herbal therapies should be regarded as drugs. Since drugs have side-effects, such events can be seen with herbals. Drug interactions although infrequent, can also occur with herbal therapies and conventional medications.
The most common dermatologic reaction from herbal therapies is allergic contact dermatitis. Herbs that are known for causing this condition include: aloe, arnica, bromelain, calendula, chamomile, goldenseal, tea tree oil and yarrow. However, more serious events have occurred including erythroderma and Stevens-Johnson syndrome from combination herbal preparations. Serious systemic adverse events have been reported with herbal therapies for the treatment of dermatological diseases as well. Most are hepatotoxic effects and some have been fatal although this is rare.Herbals that are recommended for topical use should not be ingested and vice-versa. Drug interactions that most commonly occur are due to immunomodulatory reactions, however effects on anticonvulsants and anticoagulants can occur.