St. John’s Wort – How Does It Affect Skin?

St. John’s wort is the plant species hypericum perforatum, known as a treatment of depression. It is also anti-inflammatory and traditionally used for skin wounds, scars and burns. Today, quite some skin care products have included St. John’s wort. On one hand, it can benefit skin due to its anti-inflammatory property. On the other hand, people are worried that St. John’s wort might increase their skin sensitivity to sunlight and even cause dermatitis. The fact is that ingestion and topical application of St. John’s wort have different levels of effect on skin. Ingestion of St. John’s wort is more likely to cause skin photosensitisation than topical application.

Ingestion of St. John’s wort may induce either primary or secondary photosensitisation: primary photosensitisation directly from chemicals contained in ingested St. John’s wort, or secondary photosensitisation from St. John’s wort associated damage to the liver. Liver damage usually only happens when the dose is high and continuous. Photosensitisation can then cause skin inflammation. This leads to lesions of tissue, particularly noticeable on and around parts of skin exposed to light.

Topical application of St. John’s wort, fortunately, is considered safe, especially when it is only applied at night. Researchers in Germany studied the effect of topical application of St. John’s wort on skin sensitivity to solar simulated radiation. The result showed no visible erythema. Through more sensitive photometric measurement, however, an increase of the erythema-index was detected. That being said, the skin does undergo an increase in photosensitivity. It is just not severe enough for eyes to see.

In conclusion, St. John’s wort in skin care products is safe but is highly recommended to be applied only at night. Ingestion of St. John’s wort, though effective for the treatment of depression, should be used with caution.

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