What Factors Affect the Smell of Pus?

Erin J. Hill

The smell of pus is caused almost entirely by the type of bacteria causing the underlying infection. Most odor-causing bacteria are anaerobic in nature, which means that they don’t need oxygen to survive; instead, they generate their own sulfur compounds as they grow and spread. Sulfur is usually what’s ultimately responsible for the smell that people encounter. People who have pus-filled wounds that are populated by aerobic, or oxygen-consuming, bacteria don’t usually notice any smell. The severity of the infection might also be a factor, since the body tends to produce more pus the more widespread the condition. Personal hygiene doesn’t usually impact how pus smells, but it can in certain cases. In general, medical experts recommend that anyone who is concerned about a wound’s odor get prompt treatment, since medical intervention can stop the spread of many harmful strains of bacteria and disease.

The smell of pus is determined by the type of bacteria present.
The smell of pus is determined by the type of bacteria present.

Pus Basics

Pus is a fluid that humans and many animals produce in response to an infection, and it’s usually one of the primary defenses in the immune system’s bid to flush harmful bacteria out of the body. It usually occurs most prolifically and most noticeably at wound sites; this can include simple issues like acne pimples as well as more severe infections like abscesses and stomach ulcer infections. When bacteria enter an open wound or delicate area of the skin, the body sends white blood cells to fight the infection. It also produces substances to help flush out the pathogens.

An ingrown hair with yellow pus.
An ingrown hair with yellow pus.

These substances combined with oils, dead skin cells, and other matter combined with the bacteria and white blood cells combined to form pus. On their own, these materials don’t usually have much of an odor. When people notice a stench coming from their wounds, it’s usually related more to the bacteria that the body is fighting in the first place than the composition of the mucus-like fluid itself.

Thoroughly cleansing the face with a facial wash may help treat pus in pimples.
Thoroughly cleansing the face with a facial wash may help treat pus in pimples.

Different Types of Bacteria

The type of bacteria driving the infection is usually the primary cause of any smell. This explains why some pus-filled wounds have virtually no odor at all, and why others have a very strong smell. The more sulfur-producing bacteria present, the more likely the smell of pus will be strong and offensive. In many cases, strong-smelling pus can indicate that the condition is more contagious and thus more likely to spread, since in general the concentrated bacterial volume is higher.

Pus often results from an infection.
Pus often results from an infection.

Issues of Severity

It’s often also true that severe infections smell worse than more minor ones. This is particularly the case when strong odors are coming out of what otherwise seem to be small injuries or wounds. The higher the concentration of sulfur and other foul-smelling microbial byproducts, the worse the stench is likely to be.

Role of Hygiene

The smell of pus doesn't generally have anything to do with one's hygiene or cleanliness. People are often tempted to more aggressively clean or sterilize wounds that small bad, but this isn’t usually a good idea since abrasive cleansers can aggravate the infection site. Even very clean individuals can acquire an infection with malodorous pus. Many forms of infection affect the skin when bacteria enter pores, hair follicles, or oil glands. These are relatively common and affect most people from time to time. More serious infections can occur after an injury or illness, and these are more likely to require medical treatment.

Still, hygiene can play a role. People who don’t keep the infection site clean and protected are more likely to contract secondary infections, which can often involve anaerobic strains, and compound wounds often smell worse due to the combined force of the bacteria. Even here, though, it’s not as much hygiene that’s actually causing the smell; it’s simply contributing to it.

Getting Help

It is normal for pus to have a smell to some extent, but any serious infections should be checked by a doctor. The factor that determines a serious infection isn’t usually so much whether pus has a smell, but rather the extent of other symptoms. Open wounds that are widespread or very large, or those accompanied by a fever, should generally be investigated by a doctor. In some cases antibiotics will be needed in order to kill the offending bacteria and restore health.

Pus is most common at the site of skin wounds, as the body is trying to fight an infection.
Pus is most common at the site of skin wounds, as the body is trying to fight an infection.

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Discussion Comments


I had a sebaceous cyst removed on my scalp, twice, by two different doctors. The first time, the doc cut into the cyst and squeezed out the "cottage cheese" stuff.

A few months later, the cyst returned. The second time, a different doctor cut deeper, and was able to remove the cyst whole. It has never come back.

@anon970804: That may be what you need to ask your doc to do. They have to do it when the cyst is not inflamed or infected, so that the infection doesn't spread.


Anaerobic, they say, is more prone to be foul smelling. I have one on my inner thigh, and I cannot get the doctor to do a culture, drain and clean it, and I have had it now for over two years. They just keep trying to hit it with wide spectrum products.

I have seen three internists and one dermatologist. It gets about the size of a pencil eraser, itches like mad, and also hurts. If I apply pressure, it drains an onion/garlic odor thick, sticky yellowish fluid. I clean it, and it heals. About two or three months later, it returns. What is wrong with doctors today? I have asked each one to please do a culture sensitivity test, but of course, they are the doctor! How dare I tell them how to do their jobs?


This is a weird but interesting subject. The smell of pus certainly gives us an idea about what's going on with a wound. How else would we know if a wound requires further treatment?


@burcidi-- I'm not in the medical field, so it might be best to ask your doctor. But as far as I know, a yellowish or greenish colored, and very bad smelling pus points to a serious infection.

Most simple infections like acne and skin cysts will have lighter colored discharge like you said. There won't be much of a smell either. But more serious infections make pus smell really bad.

I had a bad ear infection last year with discharge and it smelled awful. Consequently, I had to take three different courses of antibiotics to get rid of the infection.


So I guess the pus that forms on pimples are caused by aerobic bacteria and the infection isn't very serious, right?

Whenever I clean pus on pimples, I notice that the pus is clear and almost odorless. There is a slight odor, bu it's not foul, it smells like oil to me.

Is there also a connection between the color of pus and the smell of it?

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