Skip to main content

Hydrogen Sulfide in the Air and Body: Dangers and Functions

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Hydrogen sulfide gas often has a rotten egg odor.

Hydrogen sulfide gas often has a rotten egg odor.

The Significance of Hydrogen Sulfide

Hydrogen sulfide, or H2S, is a flammable, explosive, and toxic gas in the environment. It's known for its rotten egg smell and is sometimes called sour gas or stink damp. The gas is very dangerous for humans at high concentrations. In very low concentrations, it's a normal component in our bodies, where it actually has benefits. In the future, it may even be medicinally valuable.

H2S is released from decomposing organic matter, geothermal activity, and industry. It's widespread in the atmosphere but is more concentrated in some environments than in others. It's a potential problem in the oil and gas industries.

Hydrogen sulfide in the atmosphere can make breathing difficult and damage the nervous system. The more concentrated the H2S, the more pronounced its effects. It can be deadly at high concentrations.

Despite its dangers in the environment, the hydrogen sulfide that is normally present in our bodies has some useful functions. It acts as a signaling molecule in the nervous system and probably in the circulatory system as well. Recent research suggests that very low levels of the chemical may have other important health benefits in humans. Once scientists have learned more about the action of H2S in the body, it may be possible to use the chemical to treat certain health problems.

Farm animals produce a lot of manure, which needs to be removed periodically. When bacteria decompose manure, they often produce hydrogen sulfide.

Farm animals produce a lot of manure, which needs to be removed periodically. When bacteria decompose manure, they often produce hydrogen sulfide.


The information in this article is given for general interest. Hydrogen sulfide in the environment is potentially harmful and may be deadly. Hydrogen sulfide made in the body is present in a very low concentration and is safe. Low concentrations of the chemical may one day be used to treat specific disorders. Deliberate exposure to the substance today could be very dangerous.

Sources of the Environmental Chemical

Hydrogen sulfide in the environment comes from both natural and industrial sources. Bacteria produce the chemical when they decompose material that was once living, such as dead bodies and animal or human wastes. The chemical may also be released from sulfur springs and volcanic eruptions.

H2S is common in places with a large quantity of decaying organic matter and a low concentration of oxygen. It's heavier than air and tends to collect in low lying areas, including underground sewers, animal manure pits, swamps, and salt marshes.

Industries and facilities in which people may be exposed to hydrogen sulfide include oil refineries, pulp and paper mills, mines, solid waste landfills, wastewater treatment plants, and tanneries. Workers at commercial companies that handle manure may also be exposed to the chemical.

Hydrogen sulfide is also present in the gas expelled from our intestine. The chemical produces smelly flatulence if it's sufficiently concentrated. It's produced when our gut bacteria break down protein.

How Can Hydrogen Sulfide Be Detected?

H2S is an invisible gas because it's colorless. It often has a rotten egg smell at lower concentrations and a sickly sweet one at higher concentrations. After an initial odor there may be no smell at all, however. This is because the gas can deaden a person's sense of smell after they have been exposed to a high concentration for a short time or a low concentration for a long time. The smell may also be masked by the odor of other chemicals.

It's not always easy to smell hydrogen sulfide in a dangerous situation. Some people can detect the presence of H2S at lower concentrations than other people. Fortunately, hydrogen sulfide detectors can monitor the air in potentially dangerous areas so that everyone is aware of the presence of the chemical. It's important to use the detectors where they're needed.

Symptoms of Hydrogen Sulfide Poisoning

Hydrogen sulfide enters the lungs and is easily absorbed into the bloodstream. Very little is absorbed through the skin. H2S can cause severe skin irritations, however. Internal problems may be even more serious.

The symptoms produced by hydrogen sulfide poisoning depend on the concentration of the chemical and the length of the exposure. Exposure to a moderately low concentration of the chemical may cause the following symptoms. It’s important to note that the symptoms may be caused by another factor. A doctor’s diagnosis is needed.

  • eye, nose, and throat irritation
  • headache
  • nausea
  • stomach upset
  • dizziness
  • difficulty breathing due to irritation of the lungs
  • coughing
  • insomnia

Anyone experiencing one of these symptoms should visit a doctor, especially if the symptoms have no known cause, are severe, or last for a long time.

As the exposure increases, a person may experience confusion, fatigue, and a condition called pulmonary edema. In this condition, fluid collects in the air sacs of the lungs, which makes breathing very difficult. It's essential that medical aid is obtained in this situation. Exposure to a high concentration of hydrogen sulfide may cause these additional symptoms:

  • low blood pressure
  • muscle cramps
  • lack of muscle coordination
  • inability to reason
  • loss of consciousness

Loss of consciousness followed by death may be very rapid in an area containing a high concentration of the chemical.

The explosive range of hydrogen sulfide in air is 4.5 to 45.5 percent.

— OSHA (Occupational Safety and Health Administration)

Structure of a synapse (the area where a nerve impulse can travel from one neuron to another)

Structure of a synapse (the area where a nerve impulse can travel from one neuron to another)

Function in the Nervous System

Nerves transmit electrical messages, or nerve impulses, in order to control the processes that take place in our bodies. A nerve impulse is passed from one neuron (or nerve cell) to the next. There is a tiny gap between successive neurons.

When a nerve impulse reaches the end of a neuron, tiny vesicles (sac-like structures) in the neuron release a chemical called a neurotransmitter. Neurotransmitter molecules travel across the gap between neurons, join to receptors on the membrane of the second neuron, and often trigger the start of a new nerve impulse. The region where one neuron ends and another begins is called a synapse.

Some gases act as neurotransmitters. These include nitric oxide, carbon monoxide, and hydrogen sulfide. Nitric oxide is dangerous at high concentrations. Carbon monoxide is another gas that is dangerous in the atmosphere but helpful in the low concentrations found in the body.

The gaseous neurotransmitters aren't stored in vesicles like most other neurotransmitters, and they don't work in the same way. They do influence the transmission of the nerve impulse at the synapse, however. The mechanisms by which they do this are still being studied. The chemicals are often referred to as gasotransmitters.

There might be a link between garlic and hydrogen sulfide in the body.

There might be a link between garlic and hydrogen sulfide in the body.

Function in the Circulatory System

In mice, the lining of the blood vessels produces hydrogen sulfide. The chemical relaxes the muscles in the walls of the vessels, causing the blood vessels to expand. Researchers have discovered that hydrogen sulfide is also produced by the human cardiovascular system and causes blood vessels to expand. Its mechanisms of action are still being investigated. The chemical seems to have a similar function to nitric oxide, another gas that expands blood vessels.

It has been suggested—but not yet proved—that the beneficial effects of garlic on blood vessels and blood pressure are due in part to the production of hydrogen sulfide after garlic is eaten.

A very low concentration of hydrogen sulfide that is administered by a health professional might one day be used as a medicine, as described below. The chemical can't be used for this purpose yet, however. The possible uses of the substance in the future are tantalizing to consider, but safety is very important.

Possible Anti-Aging Benefits

Hydrogen sulfide may have anti-aging benefits. University scientists from China suggest that it slows aging in several ways. They say that "the evidence is mounting" that the chemical activates an enzyme called SIRT1 (also called sirtuin-1 and sirtuin deacetylase 1). This enzyme is thought to influence lifespan by a variety of methods.

The scientists also say that H2S interacts with a gene known as Klotho, which codes for a protein of the same name and is involved in anti-aging processes. In addition, research suggests that H2S reduces inflammation and is an antioxidant.

A Possible Benefit in Alzheimer's Disease

Researchers have shown that hydrogen sulfide may be neuroprotective with respect to Alzheimer's disease. Tau is a normal and important protein in our body that stabilizes cell structures called microtubules. In Alzheimer's disease, tau binds to other tau molecules instead, creating a tangle inside neurons. At least in mice, H2S can interfere with this process, as the quote below describes. The process of sulfhydration that the quote mentions decreases as we age. In people with Alzheimer's disease, the rate of decrease is more rapid than in people without the disease.

We now show that hydrogen sulfide confers neuroprotection by sulfhydrating GSK3β to inhibit its activity, thereby preventing hyperphosphorylation of Tau, a key pathogenic event in AD. Administering H2S donors improves motor and cognitive functions in a mouse model of AD.

— Daniel Giovinazzo et al, via PNAS (Proceedings of the National Academy of Sciences)

Hydrogen sulfide has helped rats with a disorder resembling Parkinson's disease.

Hydrogen sulfide has helped rats with a disorder resembling Parkinson's disease.

Potential Effects in Parkinson's Disease

It's strongly suspected that a low level of hydrogen sulfide plays a role in Parkinson's disease. Multiple studies suggest that the chemical could be useful for easing symptoms. A recent study by one scientist suggests that it can at least sometimes be harmful, however. The results might depend on where or how the chemical enters the body or on its concentration. The substance certainly seems to be worth exploring.

What Is PD?

In Parkinson's disease (PD), neurons in a part of the brain called the substantia nigra die. These cells are important because they make an essential chemical called dopamine. There seems to be more involved in the disease than this, however. Chemicals that mimic dopamine can be helpful for patients, but the supplements aren't a cure. Dopamine itself can't cross the blood-brain barrier and therefore can't be given as a medication.

Hopeful Research

Researchers have noticed that rats suffering from a disorder similar to Parkinson's disease have low levels of H2S in their brains. In multiple projects, when the rats were given an appropriate concentration of the chemical, their problems were reduced or disappeared. Though the discovery is exciting, results in rats (or other lab animals) don't always apply to humans. As in the other potential medical uses of hydrogen sulfide, many questions need to be answered and more research is needed. This research is being performed, however.

One scientist has recently raised the possibility that an excessive concentration of intestinal bacteria producing hydrogen sulfide could actually trigger Parkinson's disease. Both the concentration and the source of the chemical may be significant factors in its effects.

Hydrogen Sulfide and Suspended Animation

The term "suspended animation" as used in biology means the dramatic slowing of life processes without completely stopping them or ending life. A worm called Caenorhabditis elegans, or C. elegans, readily enters a state of suspended animation when exposed to hydrogen sulfide in the correct concentration. Its rapid movements slow and then stop. Once the H2S is removed from the air, the worm returns to its active state, apparently unharmed. C. elegans is a popular animal in anti-aging studies.

Scientists have suggested that a state of suspended animation induced by hydrogen sulfide could be useful in humans. It might be helpful in certain disease conditions and during long-distance space travel, for example. Much more research is required in relation to the feasibility of these ideas, however.

Hope for the Future

Hydrogen sulfide is a very interesting chemical. It can be dangerous and deadly in the environment or helpful as a normal component of our bodies. Hopefully, researchers will soon learn how to use the chemical to benefit our lives. Human and mammalian biology is complex and fascinating. Once we understand more details about how the chemical works, the medicinal use of hydrogen sulfide could be very helpful.


This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2013 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on June 16, 2018:

Thanks for the visit, Peggy. It's good that the wind generally removed the hydrogen sulfide from your home. It might have been an unpleasant place to live otherwise!

Peggy Woods from Houston, Texas on June 16, 2018:

We lived in Wisconsin Rapids,Wisconsin for 4 years many years ago where there were paper mills. If the wind was just right we would get that rotten egg smell occasionally from the hydrogen sulfide. Fortunately the prevailing winds generally took it away from our home.

The possible health benefits and even the effects of using hydrogen sulfide for space travel someday is informative and interesting.

Linda Crampton (author) from British Columbia, Canada on September 09, 2015:

Thank you very much for the comment, Vellur. Hydrogen sulfide is an interesting chemical, even though it's potentially dangerous.

Nithya Venkat from Dubai on September 09, 2015:

Suspended animation through hydrogen sulfide is amazing! I can still recollect the smell of hydrogen sulfide in the chemistry lab, it was awful! Well it is scary that it deadens the sense of smell when exposed to a high concentration. Informative and useful great hub, learned a lot.

Linda Crampton (author) from British Columbia, Canada on May 05, 2013:

Thank you very much for the visit, Dianna. I appreciate your comment!

Dianna Mendez on May 05, 2013:

I remember doing some science experiments in high school around this and they did smell! Great post and well done. I learned much from reading it.

Linda Crampton (author) from British Columbia, Canada on May 04, 2013:

Hi, Ingenira. Yes, hydrogen sulfide often has a horrible smell! The smell can actually be a good warning sign, but unfortunately it's not always present.

Ingenira on May 04, 2013:

It is interesting to know that Hydrogen Sulfide can be dangerous and deadly in the environment or helpful in our bodies. I have smelled it a few times, never liked it and ran away from it .... lol.

Linda Crampton (author) from British Columbia, Canada on April 23, 2013:

Thanks for the comment, Deb. The dual nature of hydrogen sulfide is certainly interesting!

Deb Hirt from Stillwater, OK on April 23, 2013:

Who would have thought that something so deadly can be so beneficial in smaller doses? interesting material, as usual!

Linda Crampton (author) from British Columbia, Canada on April 23, 2013:

What a dramatic and very sad story, Beckie. Hydrogen sulfide in the environment is a frightening substance. Thank you for the comment and for sharing the information.

Shining Irish Eyes from Upstate, New York on April 23, 2013:

Alicia - Very interesting article. I do be this gas was also responsible for wiping out an entire town years ago. They discovered underground gas seeping from the bottom of a lake. Once the gas reached the air, the lake winds blew it to residences surrounding the lakeside. Very deadly indeed.

Linda Crampton (author) from British Columbia, Canada on April 22, 2013:

Thank you very much, Bill. I appreciate your votes and the share, as always!

Bill De Giulio from Massachusetts on April 22, 2013:

Very interesting Alicia. I know the smell well. You are a wealth of knowledge. Thank you again for the education. Voted up, interesting, shared, etc...

Linda Crampton (author) from British Columbia, Canada on April 22, 2013:

Hi, Seeker7. I hope that hydrogen sulfide can be used as a medical treatment as soon as possible. Scientists need to understand more about how it works and what concentrations are necessary and safe in the body first, but it would be wonderful if it could be used as a medication. Thank you very much for the comment and the vote.

Helen Murphy Howell from Fife, Scotland on April 22, 2013:

This is a fascinating hub Alicia. All this information is new to me as I didn't know anything about this gas - well apart from the smell that is! I was really interested in H2S's relationship to Parkinson's Disease as my Dad has this - I've maybe mentioned this before.

I also found taking garlic and the health of the circulatory system fascinating as I've taken garlic for many years as it was believed that it was helpful for the heart etc.

A fascinating and thoroughly enjoyable hub - voted up!!

Linda Crampton (author) from British Columbia, Canada on April 22, 2013:

Hi, drbj. Yes, it is interesting that a substance can be both dangerous and helpful, depending on its concentration. The ability of hydrogen sulfide to put at least some animals into suspended animation is intriguing!

drbj and sherry from south Florida on April 22, 2013:

Isn't it fascinating, Alicia, how a substance like hydrogen sulfide in large concentrations can be so dangerous on one hand and perhaps extremely beneficial on the other. Guess those sci-fi movies of long-distance space travelers in suspended animation may one day be a possibility with the help of this smelly substance.

Linda Crampton (author) from British Columbia, Canada on April 22, 2013:

Thanks, Pet Artist. Yes, it's good to be aware of the possible warning signs of hydrogen sulfide presence!

Pet Artist on April 22, 2013:

Great resource. Never smelled hydrogen sulfide before, but the next time I smell rotten eggs I'll be doing more than just checking the fridge!

Linda Crampton (author) from British Columbia, Canada on April 22, 2013:

Thank you, Bill. It's good that hydrogen sulfide does have such an impressive smell. If the smell is obvious it may be a great warning system!

Bill Holland from Olympia, WA on April 22, 2013:

Great information, Alicia. I have smelled it and you are right about the rotten egg smell.