Why Are Syphilis Cases Rising in Japan? What You Should Know

Yes — and the numbers are stark. According to Japan's Ministry of Health, Labour and Welfare (MHLW), nationwide reported cases have climbed like this:

• 2018: roughly 7,000
• 2020: 5,871
• 2021: 7,978
• 2022: 13,221
• 2023: 15,055 (the highest since reporting began under the current system)
• 2024: 14,829 (slightly down from 2023, but still historically high)

MHLW itself describes the trend as a sustained increase, and notes that 2022's numbers were 6.8 times higher for men and 12 times higher for women compared to 2014.

Syphilis used to have a reputation as a disease that only affected a small, specific group of people. The data suggests that's no longer an accurate picture — it's now something anyone, regardless of age or gender, could realistically encounter.

There's no single confirmed reason for the surge. A couple of factors are backed by evidence; others are more speculative.

Syphilis is easy to spread without realizing it

This part is well documented. According to the Japan Institute for Health Security (JIHS), early symptoms — sores or ulcers — are usually painless and often clear up on their own within 3 to 6 weeks. That doesn't mean the infection is gone. It moves into a "latent" phase where there are no symptoms at all, but the bacteria is still present. During the first year of this latent phase in particular, a person can still pass it on without knowing they're infected. That combination — mild symptoms, then none at all — is a big part of why it spreads quietly.

Dating apps: a correlation worth knowing about

There's a popular theory linking the rise of dating apps and social media to the increase in syphilis. A 2020 study by Suzuki et al., published in the JMA Journal, looked at data across all 47 of Japan's prefectures and found that areas with higher dating app usage also tended to have higher syphilis rates — a statistical correlation, not proof of cause.

Left untreated, syphilis moves through distinct stages. Here's the general picture, based on MHLW's official Q&A and JIHS information.

Stage 1 (roughly 3 weeks after infection)

A painless sore or ulcer appears at the site of infection — genitals, mouth, or anus. It often heals on its own, which is exactly why it gets missed.

Stage 2 (if untreated, around 3 months in)

A faint reddish rash can appear across the body, including the palms and soles of the feet. Like stage 1, these symptoms can also fade on their own, leading people to assume they're fine.

Latent syphilis (no symptoms at all)

Once stage 1 and 2 symptoms fade, the bacteria doesn't disappear — it just goes quiet. The first year of this phase is called "early latent syphilis," and JIHS notes that while the infection is most contagious during stages 1 and 2, it can still potentially be passed on during early latency too. No symptoms doesn't mean it's resolved.

Late-stage syphilis (years to decades later)

According to a Japanese government public-information article, untreated syphilis can eventually damage the heart, blood vessels, and brain, and in some cases can be fatal. This stage is now rare, since antibiotic treatment is widely available and effective.

If a pregnant person has syphilis, it can pass to the baby — this is called congenital syphilis. According to JIHS data, congenital syphilis cases in Japan held steady at around 20 per year between 2019 and 2022, then jumped to 37 in 2023 — the highest number since Japan's current infectious disease reporting law took effect.

Congenital syphilis can cause serious problems for a baby, including developmental issues, bone abnormalities, and hearing or vision loss. That's why syphilis screening is a standard part of early prenatal care in Japan — catching it early can prevent transmission to the baby entirely.

Syphilis often causes few or no symptoms early on, so it's worth considering testing even without symptoms if any of the following apply to you. (This isn't a single official checklist — it's put together from risk factors mentioned separately by government sources and public health guidance. Talk to a healthcare provider about whether testing makes sense for your situation.)

• Your partner has been diagnosed with syphilis
• You're pregnant or trying to become pregnant
• You've had sexual contact with multiple or casual partners
• You've been diagnosed with another STI

Testing is done with a simple blood draw, so it's relatively low-hassle.

If you notice unusual symptoms after sexual contact, or you're just concerned you may have been exposed, don't wait to get tested.

About the testing window

Syphilis blood tests don't detect the bacteria directly — they detect antibodies your body produces in response. Right after infection, your body hasn't made enough antibodies yet, so a test can come back negative even if you're actually infected. This gap is called the "window period."

According to the Tokyo Association of Medical Technologists, the window period for syphilis runs roughly 3 weeks to 3 months, depending on which test is used. Non-treponemal tests (RPR) typically need about 4 weeks; treponemal tests (TP/TPHA) typically need about 2 months, and for extra certainty, some sources recommend retesting at the 3-month mark. A negative result taken too soon after exposure isn't reassuring on its own — a follow-up test later is the safer move. When you go in for testing, telling the doctor roughly when the possible exposure happened helps them judge the right timing.

Testing at a hospital or clinic

A doctor will diagnose syphilis through an exam plus a blood test. If you test positive, you can usually start treatment at the same place — no need to go elsewhere. Tests a doctor deems necessary are covered by Japanese national health insurance (check with the specific clinic for your out-of-pocket portion). Dermatology, internal medicine, and infectious disease departments are common choices, along with urology for men and gynecology for women. If you have symptoms in your mouth, an ENT specialist is also an option.

Testing at a public health center (hokenjo)

Many public health centers offer free, anonymous testing. Some offer evening or weekend testing, or women-only testing days. Details vary by location, so it's worth calling ahead.

You can search for testing and counseling locations, including for syphilis, using MHLW's official STI Testing and Counseling Map.

Syphilis is caused by the bacterium Treponema pallidum, found in fluid from sores, semen, vaginal secretions, and blood. It spreads through direct contact with these fluids on mucous membranes or broken skin — in practice, this almost always means sexual contact involving the genitals, anus, or mouth. Japan's public information campaign highlights a few key points:

Use condoms during sex

Condoms reduce direct mucous membrane contact and lower risk significantly. That said, syphilis sores can appear outside the area a condom covers, so condoms aren't a 100% guarantee — worth keeping in mind rather than relying on them as complete protection.

Don't skip protection for oral or anal sex

Since pregnancy isn't a concern with oral or anal sex, a lot of people skip condoms for these. But unprotected oral and anal sex both carry real transmission risk for syphilis and other STIs.

Fewer partners means lower risk

More sexual partners means more opportunities for exposure, in either direction. Condom use matters here too.

One more thing worth knowing: having syphilis once doesn't make you immune. You can get reinfected, so these precautions matter even after you've been treated.

According to Japan's public information portal, the standard treatment for syphilis is antibiotics — penicillin is the first-line choice, given by injection or taken orally depending on the stage of infection. In some cases, particularly more advanced ones, treatment may involve hospitalization and IV antibiotics. If you're allergic to penicillin, an alternative antibiotic can be used instead. Caught early, syphilis is curable.

The specific treatment and medication depend on your symptoms and health, so this is something to work through with your doctor rather than a fixed formula.

• Reported syphilis cases in Japan jumped from 5,871 in 2020 to 15,055 in 2023 — an all-time high — and remain elevated.
• There's no single confirmed reason for the increase. That the disease is easy to miss is a documented fact. A link between more casual sex and the spread of dating apps has also been suggested.
• Early symptoms are mild and easy to dismiss, but untreated syphilis can eventually cause serious, whole-body complications.
• Caught early, it's treatable and curable. If something feels off, testing at a clinic or public health center is a low-hassle way to find out.