I have read the Wikipedia article on coal tar. I started reading the article thinking that the principal use of it was in construction, such as in roofs and sealed roads. I found out that it was first described as a medical treatment, to be applied topically:
It may be applied to the affected area to treat psoriasis and seborrheic dermatitis (dandruff).
Coal tar
and:
It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.[10] Coal tar is available as a generic medication and over the counter.
Coal tar
and:
Coal tar is used in medicated shampoo, soap and ointment. It demonstrates antifungal, anti-inflammatory, anti-itch, and antiparasitic properties.[8] It may be applied topically as a treatment for dandruff and psoriasis, and to kill and repel head lice.
Coal tar: Uses
and:
According to the National Psoriasis Foundation, coal tar is a valuable, safe and inexpensive treatment option for millions of people with psoriasis and other scalp or skin conditions.
Coal tar: Safety
Then I found out it's described as a carcinogen.
The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer.[28][31][32] Both the U.S. Department of Health and Human Services and the state of California list coal tars as known human carcinogens.
Coal tar: Cancer
and:
Coal tar was one of the first chemical substances proven to cause cancer from occupational exposure, during research in 1775 on the cause of chimney sweeps' carcinoma.[29] Modern studies have shown that working with coal tar pitch, such as during the paving of roads or when working on roofs, increases the risk of cancer.
Coal tar: Cancer
I'm confused, because I expected it to an occupational health hazard, yet much of the article explains that it's considered important and safe in medicinal use, even by applying it directly to the skin. Actually it says both, and I wanted to get some clarification as to these two seemingly incompatible descriptions. I'm guessing there might be a different in their effects when administered as medicine as opposed to being exposed to it generally, but it does sound strange to read this sentence about something that's considered a topical medicine:
The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer.
Coal tar: Cancer