Linda Crampton is a writer and teacher with a first-class honors degree in biology. She often writes about the scientific basis of disease.
An Important and Useful Compound
Urea is a small but important compound in the living world. It’s found naturally in our body and can also be made artificially. Though it’s a waste substance as far as our body is concerned, it has some useful functions outside the body.
The liver produces urea when it breaks down amino acids from the proteins that we ingest. The urea then travels through the bloodstream to the kidneys. These remove the chemical from the blood and send it to the urinary bladder to be excreted. Doctors measure the concentration of urea in the blood to help them determine how well someone's kidneys are working.
Urea is added to skin creams to remove thickened or scaly areas and to moisturize the skin. It's helpful in the treatment of certain skin disorders. It's also a useful soil fertilizer because it's a good source of nitrogen, an important nutrient for plants. Since human urine contains urea, some people fertilize soil with urine to improve plant growth.
Urea contains only four elements—carbon, nitrogen, hydrogen, and oxygen. The lines in the diagram above represent chemical bonds. A double line represents a double bond.
Urea (Carbamide) Facts
In its solid form, urea exists as white or colorless crystals which have no odor and are highly soluble in water. The chemical is also known as carbamide when it's made in laboratories and has very low toxicity.
Some people may be familiar with carbamide peroxide, which is a mixture of artificially-made urea and hydrogen peroxide. In the correct concentration, carbamide peroxide is used to whiten teeth, to disinfect, and to remove earwax. In each of these cases, the chemical breaks down to release hydrogen peroxide, which is the active ingredient.
The use of carbamide peroxide has a historical basis. It's formulated as a solid, while hydrogen peroxide on its own is formulated as a liquid. The solid was once preferred because it could be packed into wounds. (People shouldn't try this process today.)
Urea was the first organic chemical made from inorganic ones. The reaction was carried out by Friedrich Wöhler in 1828. The discovery impressed scientists because it was thought that a mysterious "vital force" was needed to make the substances found in the human body.
In the illustration above, the carbon atom is black, the oxygen atom is red, the nitrogen atoms are blue, and the hydrogen atoms are grey.
Urea Production and Excretion
Urea production is related to the proteins that we ingest. A protein consists of chains of amino acids. The amino acids are separated from each other when protein from food is digested in the gastrointestinal tract. They are then absorbed through the lining of the digestive tract and are used to build the specific proteins needed by our body.
Excess amino acids are broken down in a process called deamination. In this process, the amino group of an amino acid (NH2) is removed and converted to an ammonia molecule (NH3). Deamination takes place mainly in the liver.
Ammonia is very toxic to cells. Ammonia molecules react with carbon dioxide in the body to make urea, which is a much safer chemical. The conversion of ammonia to urea takes place in the liver in a process known as the urea cycle. Blood vessels transport the urea to the kidneys, which remove it from the blood and send it into the urine. The urine is stored in the urinary bladder and released into the environment when we urinate. The overall process is known as excretion. A small amount of urea is released from our body in perspiration.
Concentration in the Blood
A BUN test (or Blood Urea Nitrogen test) detects the concentration of urea in the blood. If the kidneys aren’t doing their job of removing the chemical from the body, the amount of urea in the blood will increase. A BUN test can show how well the kidneys are functioning.
There are other possible reasons for an increase in the blood urea level besides kidney problems. Eating a lot of foods that are rich in protein will cause the liver to produce a large amount of urea. Dehydration will also increase the blood's urea concentration, since this depends on the amount of water in the blood. If there is less water than normal in the blood but the same amount of urea, the urea concentration will be higher than usual.
It’s also possible to have a lower than normal urea concentration in the blood. This can be caused by drinking too much water and diluting the blood, not eating much protein, or being unable to absorb enough amino acids through the wall of the small intestine due to a health problem.
One health problem that can produce a low urea concentration is celiac disease. Villi are tiny projections on the lining of the small intestine that absorb digested food. In celiac disease, the ingestion of gluten causes damage to the villi. This greatly reduces the absorption of nutrients, including protein. Gluten is a protein complex found in certain grains, including wheat, rye, and barley. While most people eat gluten with no problem, some people are gluten intolerant.
Medicinal Creams and Skin Conditions
In the body, urea is a waste substance that needs to removed. Outside the body, it's often a useful substance. For example, urea is added to some medicinal skin creams, where it often has health benefits. Urea creams can be useful in the treatment of conditions such as corns, calluses, eczema, psoriasis, and ichthyosis, which are described below. Depending on its concentration, urea either removes thickened or scaly areas of skin or makes the skin soft and supple.
- A corn is a thick and hardened area on the skin that may be painful. It often has a central core that looks different from the surroundings. It forms as a result of pressure or friction and is thought to be a protective structure. Corns often form on toes.
- A callus is also a thickened area that is formed in response to pressure. It's larger than a corn and looks the same throughout instead of having a central core. It's generally painless.
- In eczema, the skin is dry and has inflamed and itchy patches. In severe cases, the patches may also be scaly or crusty and may weep. Eczema is also known as atopic dermatitis. The skin barrier is believed to be defective in people with the disorder, making the skin susceptible to irritation. Someone with eczema may experiences flare-ups when the symptoms are present or worse than normal.
- In the most common form of psoriasis (plaque psoriasis), the skin has red patches that are itchy and develop white scales. The skin is generally thicker than in eczema. As in eczema, however, there are often flare-ups. Psoriasis is an autoimmune condition.
- In ichthyosis, the skin is dry, thickened, scaly, and sometimes flaky. In this condition, either old skin cells are shed too slowly or new ones are made too slowly. In addition, the skin barrier is defective.
Potential Benefits of Urea for Skin Problems
Someone who suspects that they have eczema, psoriasis, or ichthyosis should visit a doctor. In addition, anyone with a corn or callus that causes serious problems or becomes infected should consult their physician. The following information may be of interest, however.
With respect to eczema, DermNet New Zealand (a website run by dermatologists) says that a urea cream is "very helpful for dryness but may sting active eczema". The National Psoriasis Foundation says that a urea product can be used as a scale lifter in psoriasis. The Royal Melbourne Children's Hospital says that a urea cream can be used to loosen scales in ichthyosis. They also say that if a cream causes irritation, one with a lower concentration of urea should be tried.
Urea creams have different effects depending on the concentration of the chemical. It's important that the right concentration is chosen for a skin problem. A doctor or pharmacist should be consulted for help.
A Keratolytic Substance and a Humectant
The tough outermost layer of the skin is called the stratum corneum. This layer is made of dead cells and contains a fibrous protein called keratin. When a cream containing a high concentration of urea is applied to a thickened area on the skin, the urea weakens the attachment between the cells of the stratum corneum and dissolves keratin, allowing the area to be shed. Under these conditions, urea is said to be a "keratolytic" substance—one that causes the stratum corneum to soften and peel. The removal of the thickened skin surface is called debridement.
Urea is also hygroscopic, which means that it absorbs water from the air. Skin creams containing low concentrations of urea act as emollients. The softened skin can absorb substances better, which helps medications such as corticosteroids enter the skin. At concentrations of 2% to under 20%, urea is used as a humectant, which is a substance that retains moisture in the skin. At a concentration of 20% or higher, urea is keratolytic.
Fertilizing Soil With Urine
Urea contains forty-six percent nitrogen by weight and can be an excellent fertilizer. It’s cheaper and safer to transport and store than other nitrogen-containing products. Bacteria in soil produce an enzyme called urease. This enzyme causes urea that is added to the soil to react with water. This reaction produces ammonia and carbon dioxide. The ammonia then reacts with water to make ammonium ions, which are absorbed by plant roots.
Urine contains urea, so it could be used as a natural fertilizer. In fact, some scientists in Finland have found that urine is a very good fertilizer for soil in which beets (or beetroot) and other vegetables are planted. In a controlled experiment, they found that the beets grown in urine-fertilized soil grew significantly bigger than the beets grown in soil treated with a mineral fertilizer while still looking attractive and tasting good.
Other scientists evaluated the growth of sweet peppers in soil fertilized by urine, urea, and compost. They found that the combination of urine and compost resulted in the best growth. Other chemicals in urine besides urea might be useful for crops or might be helpful when combined with compost. It's also possible that urea is beneficial for some plants but not so helpful for others. Another factor that may affect experimental results is the concentration of a urea fertilizer and its application method.
Unlike feces, which may contain dangerous bacteria, urine is virtually sterile (unless someone has an infection of the urinary tract). It's rich in nitrogen, potassium, and phosphorus, which are elements that plants need.
Urine Fertilizers and Antibiotic Resistance
Recently, a concern about the spread of antibiotic resistance has been raised with respect to urine fertilizers. If a person donating urine has a bacterial infection somewhere in their urinary tract, bacteria that caused the infection will enter their urine. According to researchers at the University of Michigan, the bacteria that cause urinary tract infections are often resistant to certain antibiotics.
The resistant organisms would enter the soil when a urine fertilizer is used. They may come into contact with the plants that we eat. Even if the microorganisms die in the soil, their genes for antibiotic resistance may be absorbed by other bacteria in the soil. Genes are transferred between bacteria by multiple methods.
Bacterial resistance to antibiotics is a serious problem today. As a result, some diseases are becoming hard to treat. Any process that might promote the spread of resistance should be avoided. The scientists found that storing urine for twelve to sixteen months before using it as a fertilizer solved the potential problem of spreading resistance.
The scientists haven’t completely deciphered the processes occurring in the stored urine but have discovered some important information. During storage, the ammonia level in the stored urine increased, acidity decreased, and most of the bacteria released by the donors died. In addition, pieces of DNA containing genes for antibiotic resistance disintegrated during storage.
Using a Urine Fertilizer
Practitioners of urine fertilization say that the liquid must be diluted before use. The chemicals in undiluted urine are far too concentrated for the health of most plants and may injure them. Anywhere from a 1:3 to a 1:10 mixture of urine and water is suggested. In addition, the urine should be applied to the soil and not placed directly on plants. If these precautions are followed, the liquid might be a very helpful fertilizer.
Instead of diluting urine, some commercial fertilizer companies collect the liquid, sterilize it, and then extract useful components from it. Urine is reportedly a good compost activator as well as a good fertilizer.
Although it may sound strange and even repulsive, I think that the idea of recycling urine is an excellent one. The liquid contains important chemicals. It seems a shame to waste them. One of these beneficial chemicals is urea. Although it's a relatively simple molecule, urea is a very useful substance.
- Urea production in the body from the Encyclopedia Britannica
- Tooth whitening and the historical use of carbamide peroxide from the American Chemical Society
- BUN test information from the Mayo Clinic
- Treating corns and calluses from the American Academy of Dermatology.
- Treatment for eczema (atopic dermatitis) from DermNet New Zealand
- Over-the-counter topical medicines for psoriasis from the National Psoriasis Association
- Facts about ichthyosis from the Royal Melbourne Children's Hospital.
- A discussion about urine-fertilized soil from Scientific American
- Urea fertilizer information from the University of Minnesota Extension
- Aging urine fertilizers protects against the transfer of antibiotic resistance from the University of Michigan
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.
Questions & Answers
Question: Are there different types of urea or is the same type used in skin preparations and as fertilizer?
Answer: Urea is the same substance and has the same chemical formula wherever it's found. The different substances mixed with the urea in a product may react with it, modifying its structure and affecting its behaviour, however.
Question: Can urea from skin creams get into the blood system and raise BUN levels?
Answer: Diet, some medications, some diseases, and life stages (pregnancy and aging) can affect BUN levels, but I’ve never heard of urea in skin creams doing this. Based on what I’ve read, urea is absorbed to only a small extent through healthy skin. I’ve read research reports giving amounts of 7.5% and 9.5%. It would probably be a good idea to ask your doctor this question if you are concerned about your BUN level.
© 2012 Linda Crampton
Linda Crampton (author) from British Columbia, Canada on January 30, 2019:
Thank you for the visit and the comment, Annalexis.
Annalexis on January 30, 2019:
Fantastic article, and fascinating also. It gave me all the information I needed.
Linda Crampton (author) from British Columbia, Canada on January 26, 2012:
Thank you very much, teaches12345. Urea is a versatile chemical! I'm sorry that you lost your cat. I have three cats right now, but I have had two cats pass on. It is a sad experience.
Dianna Mendez on January 26, 2012:
Such interesting facts about urea! I didn't realize how it was used to help skin ailments in humans. I haven't heard of it being used as a fertilizer but then I never look at the chemical content listed on the bag. I love cats and miss my own dear little friend that passed on a couple of years ago. Loved your hub.
Linda Crampton (author) from British Columbia, Canada on January 09, 2012:
Thank you so much for the comment and the vote, kashmir56! I appreciate your visit.
Thomas Silvia from Massachusetts on January 09, 2012:
Hi Alicia my friend, this was a very interesting hub on a subject i did not know about before, thanks i enjoyed reading and learning from your well written hub .
Vote Up !!!
Linda Crampton (author) from British Columbia, Canada on January 08, 2012:
Thank you for the comment, mathira. It's very nice to meet you!
mathira from chennai on January 08, 2012:
AliciaC, thank you for useful hub.
Linda Crampton (author) from British Columbia, Canada on January 04, 2012:
Thank you for the comment and the information, CMHypno! Urea is sometimes added to animal feed. If the right enzyme is present the urea can react with water to make ammonia.
CMHypno from Other Side of the Sun on January 04, 2012:
You always find some interesting topics to write about Alicia. I also saw a programme where they were feeding urea to livestock when the grazing was poor, but only if it wasn't going to rain, as the water would cause a chemical reaction that would make the urea poisonous to the animals.