This page is general health information, not medical advice. It cannot tell you whether you have an infection. A clinician can, and the testing options on this site are a good place to start.

Syphilis is a bacterial infection that is easy to treat and easy to miss. Many people never notice the first sign, and the later signs can look like other conditions. That is why testing matters more than guessing.

This guide covers how syphilis behaves in the body, what the symptoms and rash can look like, how blood tests work, and what treatment involves. It also covers what the public health numbers say about Colorado and where Denver residents can get tested for free or at low cost.

The short answer to the question many people ask first: yes, syphilis is curable. The CDC STI Treatment Guidelines (2021) describe penicillin, prescribed by a clinician, as the preferred treatment. Early treatment prevents the later stages and their complications.

What syphilis is: the organism behind it

This section stands in for the usual ingredient breakdown. With an infection, the "key compound" is the organism itself.

Syphilis is caused by a bacterium called Treponema pallidum. It is a spiral-shaped bacterium, which is why it belongs to a group called spirochetes. The CDC describes syphilis as an infection spread mainly through direct contact with a syphilis sore during vaginal, anal or oral sex. Sores can be on or in the genitals, anus, rectum or mouth, and they are not always visible.

Syphilis can also pass from a pregnant person to a baby during pregnancy. This is called congenital syphilis, and it is the main reason prenatal screening exists.

Because the bacterium lives in the body for years if it is not treated, the infection is described in stages. Each stage has its own pattern of signs. Research suggests the stages do not always follow a tidy order, and the CDC notes that signs can be mild, brief or absent.

Syphilis symptoms by stage

The CDC groups syphilis into primary, secondary, latent and tertiary stages. A clinician can tell a person which stage a test result points to. A list of symptoms cannot do that, so read this section as background rather than a way to check yourself.

Primary stage: the sore

The first sign is usually a single small sore called a chancre. The CDC says it is typically firm, round and painless. Because it does not hurt, it can go unnoticed, especially when it is inside the vagina, rectum or mouth.

According to the CDC, the sore appears about 3 weeks after exposure on average, with a wide range. It heals on its own within a few weeks. Healing does not mean the infection is gone. The bacteria stay in the body unless treated.

Secondary stage: the syphilis rash and other signs

The syphilis rash is the best-known sign of the secondary stage. The CDC describes it as rough, reddish-brown or pink spots that can show up on the palms and soles, on the trunk, or anywhere on the body. It usually does not itch, and it can be faint enough to miss.

Other secondary signs the CDC lists include:

Fever and tiredness
Swollen lymph nodes
Sore throat
Patchy hair loss
Headaches and muscle aches
Weight loss
Moist, wart-like patches in warm areas of the body
Mucous patches in the mouth or genital area

These signs overlap with many other conditions, including common skin rashes and viral illnesses. A rash on its own does not point to syphilis, and the absence of a rash does not rule it out. Only a clinician and a blood test can sort that out.

Like the first sore, secondary signs go away without treatment. The infection then moves on quietly.

Latent stage: no signs

The CDC describes the latent stage as a period with no signs or symptoms. A person can be in this stage for years. A blood test is the only way it is found. Clinicians describe it as early latent or late latent depending on how long ago the infection likely began, which affects the treatment plan.

Tertiary stage and infection of the nervous system

Without treatment, a minority of people go on to tertiary syphilis, which the CDC says can develop years to decades later. It can affect the heart, blood vessels, brain and nervous system and can cause serious illness.

Separately, the bacterium can reach the nervous system, the eyes or the ears at any stage. The CDC guidelines call these neurosyphilis, ocular syphilis and otosyphilis. Changes in vision, hearing, balance or thinking are reasons to see a clinician promptly and to mention any possible exposure.

Is syphilis curable?

Yes. Syphilis is a bacterial infection, and the CDC STI Treatment Guidelines (2021) state it can be cured with the right antibiotic prescribed by a clinician. Penicillin is the preferred treatment at every stage.

There are two honest caveats. First, treatment stops the infection but does not undo damage that already happened, which is one reason finding it early matters. Second, being cured once does not protect against getting syphilis again. A person can be infected more than once.

The sections below explain how the diagnosis is made and what treatment and follow-up look like.

Why the national rise matters

The CDC reports that syphilis diagnoses have climbed in the United States over the past several years, including congenital syphilis. Congenital syphilis is preventable when a pregnant person is tested and treated in time, so each case points to a missed chance for care rather than an unavoidable event.

Rising numbers also mean more people are likely to meet the infection in their own community. For most readers, the practical meaning is simple: testing is routine, treatment works, and regular screening is a normal part of sexual health care.

The U.S. Preventive Services Task Force recommends screening for syphilis in people at increased risk and in all pregnant people. A clinician can help a person decide how often screening makes sense for them.

Syphilis in Denver and Colorado: what the data say

Here is what the published numbers show, with the source and year for each.

Colorado, 2023: The CDC's 2023 STI Surveillance state ranking tables list primary and secondary syphilis at 16.0 cases per 100,000 people, which is 938 cases. Those are the early, most infectious stages.
Colorado congenital syphilis, 2023: The same CDC tables list 51 cases, or 81.8 per 100,000 live births. Denver Health reported 50 cases for the same year, so the two counts differ slightly.
Denver, 2018 (older data): The Public Health Institute at Denver Health reported about 405 new syphilis cases that year in preliminary figures, up 75% over four years. This count covers all stages, not only early ones.

The Denver figure is several years old, and it is not directly comparable with the 2023 state numbers. The Denver Health Public Health Institute is the best place to ask for current local numbers. Newer Denver County rates were not available in the sources reviewed for this article.

How syphilis testing works

Syphilis is usually found with a blood test. In some cases, a clinician may also swab a sore. The CDC guidelines describe two kinds of blood tests, and they are typically used together.

Treponemal tests

Treponemal tests look for antibodies made specifically in response to the syphilis bacterium. The CDC guidelines note that these tests usually stay reactive for life, even after successful treatment. A positive treponemal test therefore shows exposure at some point, and it cannot tell by itself whether an infection is current.

Non-treponemal tests

Non-treponemal tests measure a broader immune response. They produce a number called a titer, such as 1:8 or 1:32. The CDC says this number helps clinicians judge how active an infection is and how well treatment worked, because it generally falls after successful treatment.

Non-treponemal tests can sometimes be positive for reasons other than syphilis. That is why a clinician confirms a result with the other kind of test.

Why two tests

Used together, the two tests give a clearer picture than either alone. Laboratories may run them in either order. The CDC guidelines describe both a traditional sequence and a reverse sequence, and a clinician interprets the pair of results.

Timing and window periods

Blood tests may not turn positive right away after exposure. The CDC STI Treatment Guidelines (2021) do not give one single number for every test. A clinician can say whether and when a repeat test would help in your situation, and can tell you how recent exposure affects the result.

A syphilis test is also often offered together with HIV testing. The CDC recommends HIV testing for anyone diagnosed with a sexually transmitted infection.

Syphilis treatment: what a clinician prescribes

Treatment is decided by a clinician after testing. The CDC STI Treatment Guidelines (2021) name penicillin as the preferred treatment for syphilis at all stages. The form of penicillin and the length of treatment depend on the stage and on whether the nervous system, eyes or ears are involved. This article does not cover doses or schedules, because those are set by the prescriber for each person.

Earlier stages generally need a shorter course of treatment than later stages. A clinician will explain the plan at the visit.

A possible reaction after the first treatment

The CDC notes that some people get a short-lived reaction within the first day after starting treatment for syphilis, with fever, chills, headache and muscle aches. It is called the Jarisch-Herxheimer reaction. It is not an allergic reaction. A clinician can explain what to expect and what to do about it.

Safety profile and penicillin allergy

Penicillin has been used for syphilis for decades, and research suggests the bacterium has remained sensitive to it. The main safety question is allergy. If a person reports a penicillin allergy, a clinician may evaluate it, since many reported allergies turn out not to be true allergies on testing. For some people, the clinician may choose a different antibiotic.

Pregnancy is a special case. The CDC guidelines say penicillin is the only recommended treatment for syphilis in pregnancy. A pregnant person with a penicillin allergy is typically referred for allergy evaluation and desensitization so they can still receive it.

Partners and abstaining during treatment

The CDC advises people to avoid sexual contact until treatment is complete and any sores have healed. Sexual partners may need testing and, depending on timing, treatment as well. A clinician or the health department can help with how to tell partners, and Colorado's health department can notify partners without naming the person, as many health departments do. Ask the clinic what it offers.

Colorado's expedited partner therapy position is worth knowing about. The CDC's legal status page for Colorado lists no EPT-specific statute, so a clinician is the right person to ask about options for partners.

Doxy-PEP and syphilis prevention

In 2024 the CDC issued guidance on doxycycline taken after sex (doxy-PEP) for certain groups. The CDC recommends clinicians discuss it with gay, bisexual and other men who have sex with men, and transgender women, who have had a bacterial STI in the past 12 months. Research suggests it lowers the chance of syphilis, chlamydia and gonorrhea in those groups.

Doxy-PEP is a prevention option that a clinician prescribes. It is not a treatment for syphilis that has already happened. The Denver Sexual Health Clinic's page does not state whether it offers doxy-PEP, so call to ask.

Condoms and regular testing remain part of prevention, and PrEP lowers HIV risk, though it does not protect against syphilis.

Follow-up blood tests after treatment

Treatment is not the end of the process. The CDC guidelines call for follow-up blood tests to confirm that treatment worked. For early syphilis, the guidelines describe repeat non-treponemal tests at about 6 and 12 months, and a clinician may check sooner or more often depending on the person's situation.

The CDC measures success by the titer. A drop of at least fourfold, which is a two-dilution change, is the usual sign of a good response. In some people the number falls to zero, and in others it settles at a low level and stays there. A clinician explains what a given number means.

Because treponemal tests stay positive for life in most people, a positive result on that test years later is expected after treatment. It does not mean the infection returned. This is worth knowing if a future clinician or insurer asks about it.

People living with HIV may need closer follow-up. The CDC guidelines give separate schedules, so ask the treating clinician.

Pregnancy and syphilis testing in Colorado

The USPSTF recommends syphilis screening for all pregnant people. Colorado's rule goes further on timing. According to 6 CCR 1009-1, Regulation 12, in the Code of Colorado Regulations, providers and facilities that treat pregnant people must offer syphilis testing at the first prenatal visit or in the first trimester, again in the third trimester (28 to 32 weeks), and at delivery. A fetal death after 20 weeks also triggers testing. A documented earlier test or a patient's decision to decline can change this.

House Bill 24-1456, signed June 5, 2024, directs the State Board of Health to set prenatal syphilis testing standards by rule. Anyone who is pregnant or planning a pregnancy can ask their prenatal clinician which tests are on their schedule.

Choosing a place to test: quality indicators

For a medical test, quality does not mean a brand. These are the practical things to look for.

A clinician who can treat. A site that only tests will refer you for treatment. A clinic that offers both can often start treatment sooner.
Clear information about what is tested. Ask whether syphilis is included, since some sites test only for HIV, chlamydia and gonorrhea.
Confidentiality. Reputable clinics explain who sees your results.
Posted costs or a sliding scale. When a price is not published, ask before the visit.
A plan for follow-up. Syphilis needs repeat blood tests after treatment, so a clinic that schedules them is useful.

One more thing to know: under Colorado's disease reporting rule, 6 CCR 1009-1 Appendix A, laboratories and providers report positive syphilis results to public health within 1 working day. This is how health departments follow trends and help with partner notification. It is a routine public health step.

Where to get tested in Denver

The sites below are drawn from Denver Health, the CDC's GetTested directory and the clinics' own pages. Hours and services change, so call before you go. The full list of local testing options is kept up to date on the home page, and our guide to STD testing in Denver and what it costs goes into more detail.

Denver Sexual Health Clinic

The clinic is run by the Public Health Institute at Denver Health (Denver Public Health). It is at 660 N. Bannock St., Pavilion L, 2nd Floor, Denver, CO 80204. Call 303-602-3540.

According to the Public Health Institute at Denver Health, hours are Monday to Friday, 8 a.m. to 5 p.m., with the clinic closed from 8 to 9 a.m. on the second Monday of each month. Appointments are required for all visits.

Uninsured or out-of-network patients pay on a sliding fee scale of $0 to $70, and the clinic says no one is denied care based on ability to pay. Testing-only visits without a provider are limited to gonorrhea, chlamydia, syphilis, HIV and hepatitis C. People with symptoms need a provider visit. Treatment is available at the clinic.

Denver Health community outreach testing

Denver Health also runs free, confidential walk-in testing at rotating community locations across the metro area, in English and Spanish. The page lists STD, HIV and hepatitis C testing. It does not provide exams or treatment, and it does not publish a street address or hours. Call or text 720-415-7075 for current locations. People with symptoms or a known exposure should contact the Denver Sexual Health Clinic.

HeyDenver (Colorado Health Network)

HeyDenver is at 822 E 19th Ave, Denver, CO 80218. Call 303-962-2880. Its page lists chlamydia and gonorrhea testing, rapid HIV testing, rapid syphilis testing, and hepatitis C testing case by case, along with PrEP navigation. Office hours are Monday to Friday, 9 a.m. to 4 p.m.

The site's page describes testing as free in its Spanish text but does not state a price in English. Colorado Health Network's get-tested page lists this site as testing by appointment, so confirm walk-in days when you call.

Planned Parenthood of the Rocky Mountains, Park Hill Health Center

The center is at 7155 E 38th Ave, Denver, CO 80207, phone (303) 321-2458. The CDC GetTested listing shows STD and HIV testing, hepatitis C testing and PrEP. It lists insurance and Medicaid as accepted and no appointment needed, and tells people to contact the organization about eligibility and fees. The listing does not publish hours or prices.

Clinica Tepeyac

Clinica Tepeyac is at 2101 E 48th Ave, Denver, CO 80216, phone (303) 458-5302. The CDC GetTested listing shows a sliding scale, insurance and Medicaid accepted, and appointments required. Hours are not published there, so call ahead.

STRIDE Community Health Center, Oneida

STRIDE's Oneida location is at 2255 S Oneida St, Denver, CO 80224, phone 303-778-7433, open Monday to Friday, 7 a.m. to 5:30 p.m. STRIDE's women's health page lists STI testing and treatment at some of its sites, but the Oneida page itself does not mention it, so call to confirm what is offered and what it costs.

More sites through the CDC

The CDC runs a search tool at gettested.cdc.gov that lists testing sites by ZIP code. It is a good way to find another option near you if the clinics above do not fit your schedule.

Minors and confidentiality in Colorado

Colorado law lets minors get care for sexually transmitted infections without a parent's permission. Under C.R.S. 25-4-409, a health-care provider consulted by a minor must, at the minor's request, perform an exam for a sexually transmitted infection, treat if needed, and discuss or prescribe preventive measures. Parental consent is not required, and the information is confidential except for child protection reporting. The statute sets no minimum age. For a minor 13 or younger, the provider may involve a parent or guardian.

Questions people ask

Can syphilis go away on its own?

The signs can fade without treatment, but the CDC says the infection stays in the body. Treatment from a clinician is what clears it.

Can I get syphilis again after treatment?

Yes. Being treated does not make a person immune. Regular testing is how reinfection gets caught early.

What does a syphilis rash look like?

The CDC describes secondary-stage rash as rough, reddish-brown or pink spots, often on the palms and soles, that usually do not itch. It varies a lot between people and skin tones, and it can look like other rashes. A clinician can examine it and order a blood test.

How do I talk to a partner?

Many people find it easier to keep the message simple: you were tested, here is what the clinician said, and they can get tested too. The clinic or health department can help with the wording or with notifying partners without naming you.

Key takeaways

Syphilis is a bacterial infection with four stages, and signs can be mild, painless or absent.
Two kinds of blood tests, treponemal and non-treponemal, are used together.
Syphilis is curable. Penicillin, prescribed by a clinician, is the CDC's preferred treatment.
Follow-up blood tests check that treatment worked.
Denver has free and sliding-scale testing. Call the clinic first to confirm hours, services and costs.

Syphilis in Denver: Symptoms, Testing and Treatment