Syphilis: Symptoms by Stage, Blood Tests and What to Do If Positive

In my clinic I am seeing syphilis more and more often: in teenagers, in working adults, and in people who have been with one partner for years and are only now having their first test. Surveillance data from Thailand's Department of Disease Control for 2025 shows the same picture: syphilis cases have risen steadily over the past ten years. The good news is that syphilis is easy to test for with a blood sample, and it is curable. The problem is that many people do not know they have it, because the symptoms come and then go away on their own.

What is syphilis and how is it spread?

Syphilis is caused by the bacterium Treponema pallidum. It spreads when mucous membranes or broken skin come into contact with an infectious sore or rash during vaginal, anal or oral sex. It can also pass from a mother to her unborn baby (congenital syphilis), which can cause miscarriage, stillbirth or birth defects.

Condoms greatly reduce the risk, but if a sore is somewhere a condom does not cover, such as the scrotum, the lips or around the anus, infection is still possible. Having syphilis and being cured does not give you immunity. You can catch it again.

Symptoms at each stage

Primary syphilis

About 3 weeks (range 10–90 days) after infection, a chancre appears where the bacteria entered, such as the genitals, the anus or inside the mouth. It is a firm sore with raised edges and a clean, smooth base, and it is usually painless. The lymph nodes in the groin may swell. The sore heals by itself in 3–6 weeks. Sores inside the anus or vagina often go completely unnoticed.

Secondary syphilis

About 4–10 weeks after infection, the bacteria spread throughout the body. Common symptoms are:

• A red or reddish-brown rash on the body, often on the palms of the hands and soles of the feet, usually not itchy
• Low-grade fever, tiredness, sore throat and swollen lymph nodes in several places
• Patchy hair loss, shallow sores in the mouth, or moist raised bumps around the genitals and anus (condylomata lata), which are highly infectious

These symptoms can also go away on their own, so many people mistake them for an allergic rash or an ordinary virus.

Latent syphilis

There are no symptoms at all, and it can only be found with a blood test. It is divided into early latent (infected within the past year) and late latent or unknown duration, which affects which treatment is used.

Tertiary (late) syphilis

This happens many years after infection in people who were never treated. The bacteria damage the large blood vessels of the heart, the skin, the bones or the nervous system. It is rare today, because most people have taken antibiotics at some point by chance, but it still happens.

Syphilis of the eyes, ears and nervous system can happen at any stage

This is the part many people do not know. Syphilis can spread to the eyes (ocular syphilis), the ears (otosyphilis) or the brain (neurosyphilis) even in the early stages. It does not take decades.

Syphilis blood tests and how to read them

Diagnosis uses two groups of blood tests together:

• Non-treponemal tests, such as RPR or VDRL. These are reported as a titre, for example 1:8 or 1:32. They show how active the disease is and are used to monitor treatment.
• Treponemal (specific) tests, such as TPHA, TPPA, FTA-ABS or EIA/CLIA. These show that you have been infected at some point, and they usually stay positive for life even after cure.

If there is a sore, the doctor may swab it for a PCR test that looks for the bacteria directly. A urine PCR test is not suitable for syphilis screening. See why in 14-pathogen STI PCR testing.

Who should be tested for syphilis?

• Every pregnant woman, from the first antenatal visit, with repeat tests according to guidelines
• Men who have sex with men, transgender women, people on PrEP and people living with HIV, every 3–6 months
• People with a new partner or several partners, and the partners of anyone diagnosed
• Anyone with an unexplained sore or rash, or anyone being tested for other sexually transmitted infections

Positive result: what next?

1. Do not buy antibiotics and treat yourself. Some antibiotics people commonly buy, such as azithromycin, no longer work against syphilis because of resistance.
2. See a doctor to work out the stage, and get tested for HIV and other infections at the same time.
3. Get treatment according to the stage. The main medicine is long-acting benzathine penicillin G by injection. Details are in Syphilis treatment and follow-up blood tests.
4. Tell your partners so they can be tested and treated. I can help you think about how to tell them. Read When your partner has an STI.
5. Avoid sex until treatment is complete and any sores or rash have healed.

If the result weighs on you, please know that syphilis is a treatable infection. It says nothing about your worth as a person. You may find it helpful to read Feeling guilty after an STI.

Prevention

• Use condoms every time, and have regular blood tests based on your risk.
• Treat partners at the same time to break the cycle of reinfection.
• For some groups who get reinfected often, Doxy-PEP may be an option on a doctor's advice.

How the clinic can help

At Dr. Kris Clinic we offer syphilis blood tests, both screening and specific tests. I interpret the results together with your past history, provide treatment, monitor your titres, and care for your partner at the same time, all in private. English-speaking consultations are available. If you have symptoms affecting the eyes, ears or nervous system, I will refer you to hospital immediately, because you will need intravenous treatment.