What Are the Symptoms of an Infection?

Common Signs and Features by Organ System

An infection is the invasion of the body by a disease-causing organism called a pathogen. Infections can be caused by a wide range of pathogens, including bacteria, viruses, fungi, and parasites, and can develop in any organ system of the body.

Infections can be classified in a number of different ways. They may be localized (affecting a specific part of the body) or systemic (affecting the body as a whole).

What is an Infection?

Verywell / Theresa Chiechi

Some infections are contagious (spread directly or indirectly from person to person, like the flu). Others may be spread by an animal or insect or picked up from the environment.

There are also primary infections in which healthy host tissues are invaded and secondary infections that arise as a complication of another disease or condition. This article discusses general symptoms of infections and symptoms when different parts of the body have an infection.

Classifying Symptoms

The signs and symptoms of an infection can also vary. Some are generalized and nonspecific, like fever, fatigue, and chills. Others are specific to the body part, such as a rash, coughing, or swelling of a joint.

When diagnosing an infection, doctors will want to hone in on the part of the body in which the infection was established. By recognizing the characteristic signs and symptoms, they can order tests and procedures to diagnose the cause and prescribe the correct treatment definitively.

These include antibiotics for bacterial infections, antivirals for viral infections, antifungals for fungal infections, and antiparasitics for parasitic diseases.

General Symptoms

Whenever an infection is established, the body's first-line response is inflammatory. Inflammation is the body's way of defending itself against disease while promoting the healing of affected tissues. Inflammation is characterized by five cardinal signs: redness, swelling, heat, pain, and the temporary loss of tissue function.

During an infection, people often experience nonspecific, generalized symptoms as a result of the underlying inflammatory response. The signs and severity can differ based on the affected organ system but may include:

Acute vs. Chronic

Acute infections can cause acute inflammation (characterized by rapid onset and resolution), while chronic infections can cause chronic inflammation (characterized by persistence and the progressive destruction of tissues by the inflammatory process).

Respiratory Tract

The respiratory tract is the passage through which air passes from the mouth and nose to the lungs. An infection can develop in the upper respiratory tract (involving the sinuses, nasal passages, pharynx, and larynx) or the lower respiratory tract (involving the trachea and the bronchi, bronchioles, and alveoli of the lungs).

Upper Respiratory Tract

Upper respiratory tract infections (URTIs) include the common cold, influenza (the flu), laryngitis (infection of the voice box), pharyngitis (sore throat), tonsillitis (infection of the tonsils), and sinusitis (sinus infection).

Symptoms can vary based on the part of the tract affected but often include:

  • Sneezing
  • Runny nose
  • Nasal congestion
  • Nasal discharge
  • Scratchy or sore throat
  • Pain when swallowing
  • Coughing
  • Sinus pain

Fever, headaches, and malaise are also common.

Lower Respiratory Tract

A lower respiratory tract infection (LRTI) is often used as a synonym for pneumonia but can apply to any infection in the trachea or lungs, including acute bronchitis and bronchiolitis. These infections can be bacterial, fungal, or viral, including influenza, tuberculosis, and COVID-19.

Symptoms of an LRTI may include:

Severe LRTIs can cause cyanosis, a condition in which the lips and skin can turn a bluish color due to the lack of blood oxygen.

Urinary Tract

The urinary tract is the system through which urine is excreted from the body and includes two kidneys, two ureters, a bladder, and a urethra. A urinary tract infection (UTI) affects any part of this system, including urethritis (infection of the urethra), cystitis (bladder infection), or acute pyelonephritis (kidney infection).

Symptoms of a UTI can differ based on the location of the infection but may include:

Severe UTIs may cause fever with chills as well as nausea and vomiting.

Brain and Spinal Cord

The central nervous system (CNS) is comprised of the brain and spinal cord. Infections of the CNS typically involve the brain (encephalitis) or the protective membrane around the brain and spinal cord (meningitis).

Symptoms of a brain or spinal cord infection can differ by severity and may include:

  • Sudden fever
  • Stiff neck
  • Severe headache
  • Difficulty concentrating
  • Light sensitivity
  • Sleepiness
  • Nausea or vomiting
  • Confusion
  • Difficulty walking
  • No appetite or thirst
  • Seizures


Primary encephalitis is most often caused by viruses like herpes simplex virus (HSV). While viruses are also the most common cause of meningitis, bacterial causes tend to be more severe and even life-threatening.


Bloodstream infections are most commonly associated with bacteria (bacteremia). They often develop as a secondary infection to pneumonia, meningitis, or cellulitis, or when bacteria enter the bloodstream during surgery or intravenous drug use.

Septicemia is the term used to describe a serious blood infection. Sepsis occurs when the response to the infection causes organ damage.

Symptoms of a blood infection may include:

  • Fever and chills
  • Rapid breathing
  • Rapid heart rate
  • Low body temperature
  • Clammy skin
  • Extreme fatigue and weakness
  • Nausea or vomiting
  • Decreased urination
  • Difficulty breathing
  • Pale, blotchy, or bluish skin
  • Changes in mental state
  • Fainting or unconsciousness

Septic Shock

If not treated immediately and aggressively, sepsis can lead to septic shock in which an extreme drop in blood pressure can cause organ failure and even death.


Liver infections are primarily viral in nature, caused by the viruses hepatitis A, B, C, D, or E. Some acute hepatitis infections resolve on their own without treatment. Others may become chronic and lead to progressive liver injury (particularly with hepatitis B and hepatitis C).

Hepatitis simply describes the inflammation of the liver, whether by infection or other causes. Symptoms of viral hepatitis may include:

  • Fever
  • Fatigue
  • Loss of appetite
  • Nausea or vomiting
  • Abdominal pain
  • Dark urine
  • Light-colored stools
  • Joint pain
  • Jaundice (yellowing of the skin or eyes)

Chronic hepatitis infection can lead to cirrhosis, liver failure, and liver cancer.

Gastrointestinal Tract

The gastrointestinal tract is the passage through which food enters the body and exits as stool. It includes the mouth, esophagus, stomach, small intestine, large intestine (colon), and anus.

Gastrointestinal infections are viral, bacteria, or parasitic infections that cause gastroenteritis, an inflammation of the stomach and intestines. The pathogens are often transmitted by contaminated food and shared personal items.

Common causes of infectious gastroenteritis include bacteria like Escherichia coli and Salmonella, viruses like rotavirus and norovirus, and parasites like Giardia lamblia and Cryptosporidium.

Symptoms of a gastrointestinal tract infection may include:

  • Abdominal cramps
  • Diarrhea
  • Nausea and vomiting
  • Fever
  • Muscle aches
  • Headache
  • Fatigue


Dehydration is a common complication of diarrhea in people with severe gastroenteritis, sometimes requiring emergency medical care with intravenous fluids.

Some bacteria and parasites are also known to cause infectious dysentery, a severe infection of the intestines causing vomiting and bloody stools.


Otitis is the general term for an infection of the ear. It may involve the external ear (otitis externa or "swimmer's ear"), middle ear (otitis media), or inner ear (otitis interna or labyrinthitis).

Ear infections can be caused by bacteria like Staphylococcus aureus or Pseudomonas aeruginosa, viruses like herpes simplex virus type 1, or fungi like Candida albicans or Aspergillus. Some ear infections are secondary to an upper respiratory tract infection like strep throat.

Symptoms can vary by the location of the infection, with some causing minor discomfort and others resulting in severe pain and disability.

Symptoms of an ear infection may include:

  • Ear pain
  • Ear redness or swelling
  • Muffled hearing
  • Fever
  • Headache
  • Ringing in the ears
  • Drainage of fluid from the ear
  • Swollen lymph nodes in the neck
  • Vertigo (a dizzy feeling like your surroundings are spinning)
  • Loss of balance and falling
  • Nausea or vomiting

Symptoms are generally more severe the deeper the infection is within the ear. Some severe inner ear infections can cause nystagmus (uncontrollable eye movements), crippling vertigo, and even permanent hearing loss.


Eye infections are common because the eye is vulnerable to pathogens that are easily transmitted by hand-to-eye contact or an eye injury. These include infectious conjunctivitis ("pink eye"), infectious keratitis (affecting the cornea), and infectious endophthalmitis (affecting the inner eye).

Eye infections are frequently associated with viruses like adenovirus and herpes simplex virus. Bacterial causes include Staphylococcus aureus and Streptococcus pneumonaie as well as sexually transmitted infections (STIs) like gonorrhea and chlamydia.

An eye infection often involves only one eye but can easily spread to both. Symptoms may include:

  • Deep pink or red color in the white of the eye
  • Eye swelling, itchiness, or burning
  • Eye pain
  • Excessive tearing
  • A feeling of having something stuck in the eye
  • Swelling of the eyelid
  • Sensitivity to light
  • Decreased vision
  • Eye discharge


Bacterial infections, particularly those affecting the cornea or inner eye, are especially worrisome because they can lead to permanent vision loss if not treated appropriately.


Vaginal infections typically involve the overgrowth of fungus or bacteria that commonly reside on vaginal tissues, leading to vaginal inflammation (vaginitis).

These include yeast infections that arise from the overgrowth of the fungus Candida albicans and other types of Candida. Bacterial vaginosis (BV) similarly occurs when levels of a bacteria called lactobacillus are low, allowing "unfriendly" bacteria to thrive and proliferate. Some STIs can also cause vaginitis.

Signs and symptoms of a vaginal infection may include:

  • Vaginal redness and swelling
  • Itchiness, often intense
  • Thick, white or gray vaginal discharge
  • Burning or pain when urinating
  • A strong, fishlike odor (especially with BV)
  • Pain with sex
  • Swollen lymph nodes in the groin

A pelvic exam with a vaginal swab may be needed to positively diagnose the infection and dispense the appropriate treatment.

Sexually Transmitted Infections

Sexually transmitted infections are those that can be transmitted by vaginal sex, anal sex, or oral sex. These include chlamydia, genital herpes, gonorrhea, HIV, human papillomavirus (HPV), syphilis, and trichomoniasis.

Symptoms vary not only by sex but also by the site of the infection. In some cases, there may be no symptoms at all.

If you are sexually active, you may want to see a doctor about an STD screen if you develop some of the following telltale symptoms:

  • Pain or burning when urinating
  • Vaginal discharge, often with a bad odor
  • Discharge from the penis
  • Swollen or tender testicles
  • Genital itchiness
  • Rectal itch, discharge, or bleeding
  • Genital sores or blisters
  • Genital warts
  • Pelvic pain
  • Enlarged lymph nodes (particularly those in the neck or groin)
  • Pain and/or bleeding during sex
  • Bleeding between periods

Shared Symptoms

Most of the symptoms of STIs can occur with nonsexually transmitted diseases as well as noninfectious conditions affecting the genitourinary tract. Even so, sexually transmitted infections should be considered if you have risk factors for STIs.


Skin infections are caused by an almost encyclopedic array of pathogens. As the human body's largest organ, the skin is vulnerable to infection whenever it is broken or compromised or your immune system is suppressed.

These include bacterial infections like impetigo and folliculitis, viral infections like shingles (herpes zoster) and warts, and fungal infections like athlete's foot (tinea pedis) and ringworm. Some are readily treatable with over-the-counter medications; others, like necrotizing fasciitis, are difficult to treat and require aggressive medical intervention.

Signs of a skin infection may include:

Fever and chills can sometimes accompany an acute skin infection, along with increasing pain, tenderness, and swelling.

Skin infections can often be differentiated by the location and characteristics of rashes, lesions, and sores—including whether they are generalized or localized, flat or raised, have well-defined or ill-defined borders, or cause crusting, itching, pitting, or flaking.

These characteristics can help direct the diagnosis and ensure the correct treatment plan.


An infection may be caused by different types of organisms including bacteria, viruses, fungi, and parasites invading body tissues. This sets off an inflammatory reaction, which can produce general symptoms such as a fever, chills, and body aches. Symptoms may also be specific for the part of the body or organ that is infected.

A Word From Verywell

Although you may have telltale signs of an infection, the symptoms alone may not be enough to pinpoint the exact cause. And this can be a problem if you treat, for example, a viral infection with an antibiotic or a bacterial infection with an antiviral.

Even certain "mild" infections, like bacterial conjunctivitis or acute bronchitis, can turn serious if left untreated or treated inappropriately.

It is important, therefore, to see a doctor if an infection is persistent or worsening or causing respiratory symptoms, changes in urination, hearing or visual impairment, or any other symptom that seems unusual or unexplained.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By James Myhre & Dennis Sifris, MD
Dennis Sifris, MD, is an HIV specialist and Medical Director of LifeSense Disease Management. James Myhre is an American journalist and HIV educator.