Dizziness, fatigue, and irritation of mucous membranes have been reported in people exposed to selenium
1.5 How can selenium affect my health?

The general public rarely breathes high levels of selenium, although some people may be exposed to selenium dust and
selenium compounds in workplace air. Dizziness, fatigue, and irritation of mucous membranes have been reported in
people exposed to selenium in workplace air at concentrations higher than legal levels. In extreme cases, collection of
fluid in the lungs (pulmonary edema) and severe bronchitis have been reported. The exact exposure levels at which
these effects might occur are not known, but they become more likely with increasing amounts of selenium and with
increasing frequency of exposure.

The normal intake of selenium by eating food is enough to meet the Recommended Daily Allowance (RDA) for this
essential nutrient. However, as discussed in Chapters 2 and 3 of this profile, selenium compounds can be harmful at
daily dietary levels that are higher than needed. The seriousness of the effects of excess selenium depends on how
much selenium is eaten and how often. Intentional or accidental swallowing of a large amount of sodium selenate or
sodium selenite (for example, a very large quantity of selenium supplement pills) could be life-threatening without
immediate medical treatment. Even if mildly excessive amounts of selenium are eaten over long periods, brittle hair and
deformed nails can develop. In extreme cases, people may lose feeling and control in arms and legs. These health
effects, called selenosis, were seen in several villages in China where people were exposed to foods high in selenium
for months to years. No human populations in the United States have been reported with long-term selenium poisoning,
including populations in the western part of the country where selenium levels are naturally high in the soil. Because
most people in the United States eat foods produced in many different areas, overexposure to selenium in food is
unlikely to occur.

Upon contact with human skin, industrial selenium compounds have been reported to cause rashes, redness, heat,
swelling, and pain. Brief, acute exposure of the eyes to selenium dioxide as a dust or fume in workplace air may result in
burning, irritation, and tearing. However, only people who work in industries that process or use selenium or selenium
compounds are likely to come into contact with levels high enough to cause eye irritation.

Based on studies done until 1987, the International Agency for Research on Cancer (IARC) determined that selenium
and selenium compounds could not be classified as to their ability to cause cancer in humans. However, since then, the
EPA has determined that one specific form of selenium, called selenium sulfide, is a probable human carcinogen.
Selenium sulfide is the only selenium compound shown to cause cancer in animals. Rats and mice that were fed
selenium sulfide daily at very high levels developed cancer. Selenium sulfide is not present in foods, and it is a very
different chemical from the organic and inorganic selenium compounds found in foods and in the environment. Also, if
introduced into the environment, selenium sulfide does not dissolve readily in water and would probably bind tightly to
the soil, further reducing any chance of exposure. Because selenium sulfide is not absorbed through the skin, the use of
anti-dandruff shampoos containing selenium sulfide is generally considered safe.

Very high amounts of selenium have caused decreased sperm counts, increased abnormal sperm, changes in the
female reproductive cycle in rats, and changes in the menstrual cycle in monkeys. The relevance of the reproductive
effects of selenium exposure in animals studied to potential reproductive effects in humans is not known. Selenium
compounds have not been shown to cause birth defects in humans or in other mammals