It can spread through direct contact with infectious sores during vaginal, anal, or oral sex.
The first noticeable sign may be a small, usually painless sore called a chancre.
It can develop on the genitals, around the anus, or inside the mouth.
Because the sore may not hurt, some people do not notice it.
The sore can disappear without treatment, but this does not mean the infection has gone away.
Syphilis may then progress through different stages.
During the secondary stage, some people develop a rash, including one that may appear on the palms of the hands or soles of the feet. Other possible symptoms include swollen lymph nodes, fever, and fatigue.
Later, the infection may enter a latent stage in which there are no visible symptoms.
Without appropriate treatment, syphilis can eventually damage the nervous system, cardiovascular system, and other organs.
Fortunately, syphilis is curable with appropriate antibiotic treatment, especially when identified early.
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4. Genital herpes: Painful sores that may return
Genital herpes is usually caused by herpes simplex virus type 2, although herpes simplex virus type 1 can also cause genital infection.
The infection may produce small blisters or painful sores around the genitals, anus, or surrounding skin.
Some people experience itching, tingling, or burning before the sores appear.
Others have very mild symptoms that are mistaken for ordinary skin irritation.
After the initial infection, the virus remains in the body and may reactivate.
Outbreaks can recur, although their frequency and severity vary considerably.
There is currently no cure that eliminates herpes from the body.
However, antiviral medicines can help shorten outbreaks, reduce symptoms, and lower the risk of transmission.
5. Human papillomavirus: An infection associated with certain cancers
Human papillomavirus, commonly known as HPV, includes many different viral types.
Some types can cause genital warts, while others are associated with cervical, anal, penile, vulvar, vaginal, and oropharyngeal cancers.
Most HPV infections clear naturally through the body's immune response.
However, persistent infection with certain high-risk types can lead to abnormal cell changes.
These changes may take years to develop into cancer.
One important preventive measure is HPV vaccination.
Screening for cervical cancer is also essential because it can identify precancerous changes before they become more serious.
The most important lesson is that different infections produce different symptoms, and some produce none at all.
There is no single rash, bump, or skin mark that can identify every sexually transmitted infection.
When exposure is possible, testing is much more reliable than waiting for visible symptoms.
Chapter 3: What Happens to the Body When an STI Is Left Untreated?
The consequences of an untreated sexually transmitted infection can vary significantly.
Some infections disappear without causing long-term complications, while others can gradually damage reproductive organs or affect other parts of the body.
The problem is that complications do not always appear immediately.
Someone may acquire an infection, experience few symptoms, and continue their normal activities without realizing that a medical problem is developing.
Understanding these potential consequences is an important reason to seek testing after possible exposure.
1. Pelvic inflammatory disease in women
One of the important complications associated with untreated chlamydia and gonorrhea is pelvic inflammatory disease, commonly known as PID.
PID occurs when bacteria spread from the vagina or cervix into the upper reproductive tract.
The infection can affect the uterus, fallopian tubes, and surrounding pelvic structures.
Some women experience lower abdominal pain, fever, unusual discharge, pain during sexual activity, or bleeding between periods.
Others may have relatively mild symptoms.
The danger is that inflammation can damage the fallopian tubes.
Scar tissue may develop, making it more difficult for an egg to travel from the ovary toward the uterus.
This can increase the risk of infertility and ectopic pregnancy.
An ectopic pregnancy occurs when a fertilized egg implants outside the uterus, most commonly in a fallopian tube.
It is a potentially life-threatening medical emergency.
Women experiencing sudden severe abdominal pain, fainting, or significant bleeding should seek emergency medical attention.
Early diagnosis and appropriate treatment of reproductive tract infections can reduce the risk of complications.
2. Fertility problems in men
Men can also experience reproductive complications following certain untreated infections.
Chlamydia and gonorrhea can cause inflammation of the epididymis, the structure that stores and transports sperm.
This condition is called epididymitis.
Symptoms may include pain, swelling, tenderness, and warmth in one or both testicles.
Some infections can also cause inflammation in other parts of the reproductive system.
Although not every episode leads to infertility, severe or untreated complications may affect reproductive function.
Sudden testicular pain requires urgent medical assessment because conditions such as testicular torsion must be ruled out.
3. Pregnancy complications
Certain sexually transmitted infections can affect both the pregnant woman and the developing baby.
Syphilis is particularly important.
When a pregnant woman has untreated syphilis, the infection can pass to the fetus through the placenta.
This may result in miscarriage, stillbirth, premature birth, or congenital syphilis.
Congenital syphilis can cause serious problems in newborns, including bone abnormalities, anemia, liver and spleen enlargement, and neurological complications.
Other infections can also affect pregnancy.
Untreated gonorrhea and chlamydia may contribute to pregnancy complications and can sometimes be transmitted to the baby during childbirth.
HIV and hepatitis B also require appropriate screening and management during pregnancy.
The important point is that prenatal screening and timely treatment can prevent many serious outcomes.
4. Increased vulnerability to other infections
Certain STIs can increase the risk of acquiring or transmitting HIV.
For example, genital ulcers and inflammation can disrupt the protective barriers of the skin and mucous membranes.
This may make it easier for HIV to enter the body during sexual exposure.
At the same time, untreated HIV can progressively damage the immune system.
Without treatment, the infection can eventually develop into AIDS, the most advanced stage of HIV disease.
Modern antiretroviral therapy has transformed HIV care.
People who receive effective treatment can live long, healthy lives. Those who maintain an undetectable viral load do not sexually transmit HIV.
This is commonly summarized as U=U, meaning Undetectable equals Untransmittable.
5. Long-term damage to the nervous system and heart
Untreated syphilis can eventually affect organs far beyond the reproductive system.
In some people, the infection progresses to later stages and damages the nervous system, eyes, ears, or cardiovascular system.
Possible complications include neurological problems, vision changes, hearing loss, and damage to major blood vessels.
These complications may take years to develop.