Palo santo incense—wooden sticks that are lit to smolder, filling a room with aroma—is often called healing. These incense supposedly not only relax and help cope with insomnia, but also disinfect the air around it. We checked whether this is actually true.

Here is what they write about this in one of the articles on the Yandex.Zen portal:

“The smoke of palo santo is medicinal, it reduces the number of bacteria in the air. A 2007 scientific study published in the journal Ethnopharmacology found that medicinal smoke can almost completely eliminate bacteria in the air in a confined space. One hour of burning medicinal smoke reduced airborne bacteria by 94%, and the cleansing effect lasted 24 hours indoors.”

Palo santo means "holy tree" in Spanish. This tree (Bursera graveolens) grows in North and South America; its oil is often used in cosmetology. Some peoples living in South America also use this tree for ritual and medicinal purposes: for example, for relaxation.

Palo Santo has a pleasant smell, and its smoldering wood chips are now often used as incense. Smoke spreads throughout the room and words some users, purifies the air, killing up to 94% of bacteria. At the same time, the authors of these statements refer to the same study that the Yandex.Zen user writes about.

The same effect is often attributed to sage. Claims that its smoke disinfects the air met even in the headlines of some media. Moreover, the links lead to the same study.

In 2007, the journal Ethnopharmacology actually published article, in which scientists talked about how the smoke of medicinal herbs affects the bacteria in the room. The results of the study indeed showed that smoke kills up to 94% of bacteria in a room, and the effect lasts more than 24 hours.

However, the researchers weren't really testing the effects of palo santo or sage. The experiment involved a large mixture of herbs and wood called havan samagri, which is commonly used in Hinduism for ritual cleansing of rooms.

In the study, the authors list the ingredients that were involved in the herbal bundle: there is no palo santo or sage. Most of the plants are characteristic species of India. Palo santo grows mainly in North and South America and is used in traditional medicine mainly in Ecuador.

Thus, burning certain herbs (or a mixture of herbs) can actually reduce the amount of bacteria in the air. But there is no data confirming this information about palo santo.