Syphilis: Common Questions, Facts You Should Know, and How to Prevent Infection

Doctors and the media have been warning people about syphilis lately. Syphilis is a sexually transmitted infection (STI), and it is spreading more widely because it is transmitted easily — no less than HIV. This is especially true among people who often have risky sexual contact and do not use condoms for protection. Today, let's take a closer look at syphilis.

What is syphilis?

Syphilis is a contagious infection caused by a type of bacteria. These bacteria most often enter the body through sexual contact. Once they get into the body, they spread through the bloodstream and can live in almost any part of the body. However, if it is detected early, syphilis can be completely cured.

Causes of syphilis

Syphilis is caused by a bacterium called Treponema pallidum and is classified as a sexually transmitted infection. It can also be passed on by sharing needles or by receiving blood from someone who is infected. The bacteria spread through direct contact with an infectious sore during sex, entering the body through the mucous membranes or through wounds, such as those in the mouth, the lining of the eye (conjunctiva), the vagina, the urethra, and the anus. On top of this, a pregnant woman who is infected can also pass the infection to her baby in the womb.

Symptoms of syphilis

The symptoms of syphilis occur in four stages: the primary stage, the secondary stage, the latent stage, and the tertiary stage.

Choose STI testing that fits your situation * Prices and free services vary by provider. Please check the details before booking. View testing locations → 05

Syphilis, stage one:

In the first stage of infection, the person develops a small, firm, red sore that doctors call a "chancre." It appears on the vagina, the genitals, under the foreskin of the penis, the anus, or the mouth. Some people may have only one sore, while others have several. The sore is painless. It usually appears about 10 days to 3 months after the bacteria enter the body, though in some cases it can appear in as little as 3 weeks. After that, these symptoms clear up on their own within 3–6 weeks. However, the syphilis bacteria are still spreading inside the person's body.

Syphilis, stage two:

These symptoms appear about 1–3 months after the chancre heals. The person develops a rash and raised bumps that look like warts on the torso, the palms, the soles of the feet, and the genitals. Some people may have a rash on other parts of the body as well. The rash does not itch, but it comes with muscle aches, fever, sore throat, fatigue, hair loss, or abnormally swollen lymph nodes. These symptoms may clear up on their own or come back again.

• Fever
• Sore throat
• Swollen lymph nodes
• Some people have muscle aches

Latent (quiet) stage of syphilis:

The latent stage develops in the more than 30% of people who do not receive correct, appropriate treatment during the second stage, and from there the disease can progress to the third stage more easily. In the latent stage, the syphilis bacteria remain in the body for many years without causing any clear symptoms.

Syphilis, stage three:

This is the final stage for a person with syphilis. It occurs when the person does not receive correct and timely treatment. It usually appears 10–20 years after infection, when the bacteria have spread throughout the body and cause more and more damage. This stage produces clear symptoms such as dementia, blindness, paralysis, deafness, heart disease, and sexual dysfunction, and it can ultimately be fatal.

Find STI testing near you and get care early * Prices and free services vary by provider. Please check the details before booking. Find STI testing → 01

Treating syphilis

Today, syphilis is treated mainly with antibiotics in the penicillin group. In Thailand, most treatment uses penicillin G, which comes in several forms, such as:

• Benzathine penicillin G
• Aqueous penicillin G

The doctor injects the medication, basing the treatment on how long the person has been infected and using their judgment for each individual case.

Preventing syphilis

To avoid getting syphilis, avoid sexual contact with anyone who has the infection, and always use a condom for protection. Couples who are planning to marry should have a thorough medical checkup and get tested for syphilis before the wedding and before planning a pregnancy. If an infection is found, it is far better to plan for treatment and a full cure than to face health problems — passing the infection to a partner and to the baby in the womb, which could leave the baby with disabilities or lead to death later on.

Questions worth knowing about syphilis

What kind of germ is syphilis, and how does it enter the body?

• Answer ☞ Syphilis is a type of bacteria that enters the body through wounds on the skin or through the mucous membranes.

If you only have outercourse (external contact), can you still get syphilis?

• Answer ☞ Many people think that syphilis can't be passed on without penetration. But external activities — such as oral sex or licking the genitals with the tongue — can come into direct contact with the syphilis bacteria on the mouth, tongue, vagina, anus, and so on, and can still lead to infection.

If you get syphilis, what symptoms will you have?

• Answer ☞ Not everyone shows symptoms of syphilis right away. It depends on your physical condition, how strong you are, and how often you are exposed to risk. Once a person is infected, the bacteria can stay latent for many years. The best thing to do is to get tested and treated promptly as soon as you know you have been at risk.

What does a syphilis rash look like?

• Answer ☞ Before a syphilis rash appears, there is first a chancre. This kind of sore has a raised, firm edge and is painless when pressed. It is most often found on the genitals of both men and women, or on the lips. You may notice it anywhere from a little over a week to about 3 months after unprotected exposure. The chancre can heal on its own even without treatment. Then, about a month and a half to two months later, a rash may appear on the torso, hands, feet, or elsewhere on the body, along with headache, fever, nausea and vomiting, and body aches. These symptoms, too, can clear up on their own within 1–3 months.

If you get syphilis and receive treatment, can it be fully cured? Can it come back?

• Answer ☞ If you know you have been at risk of syphilis and it is detected early, there is a good chance it can be completely cured. But if the bacteria have been latent for a long time, a doctor needs to diagnose you and treat you according to the stage of the disease, which may take longer than a typical case. People with syphilis must take their medication strictly and keep every doctor's appointment. Even after you have recovered from syphilis, it is recommended that you get retested every 3 months for 3–5 years after treatment, because some bacteria may still be hidden in the body — or you may be at risk of a new infection.

Does having syphilis mean you will get AIDS?

• Answer ☞ Syphilis and HIV are two different infections. However, if you already have syphilis, you are up to 5 times more likely to contract HIV than someone who does not. However, taking antiretroviral therapy (ART) consistently — even to an undetectable viral load (U=U) — prevents passing HIV to others, but it does not protect against syphilis or other STIs. People living with HIV still need to use condoms every time and get tested regularly.

Who should get tested for syphilis?

• Answer ☞ People at higher risk include those who change sexual partners often, do not use condoms, and do not protect themselves; people who think their partner may be at risk of syphilis; and parents who are planning to have a child.

How can you avoid getting syphilis?

• Answer ☞ Protect yourself by using condoms for every sexual activity. Learn to pay attention to your partner, or have sex only with a partner you are confident is free of infection. Avoid using sex services or changing partners often.

Syphilis is a dangerous sexually transmitted infection. Left untreated, it can cause serious complications. The best way to prevent syphilis is to use a condom every time you have sex.

Verified references

Links and relevance to the article’s main topic were reviewed on 13 August 2026. Each source supports only the scope stated in the original document and does not replace personalised medical, legal, or service advice.

1. CDC: About Syphilis Accessed 13 August 2026
2. CDC: STI Treatment Guidelines Accessed 13 August 2026