Chancroid spreads primarily through sexual contact with someone who has an active infection. The bacterium responsible, Haemophilus ducreyi, cannot penetrate intact skin on its own. It needs tiny breaks in the skin surface, like the micro-abrasions that naturally occur during sex, to enter the body and establish an infection.
How the Bacteria Enter Your Body
During sexual contact with an infected person, H. ducreyi passes from an open ulcer to your skin. The bacterium slips through small tears or disruptions in the skin’s outer layer, the kind of microscopic damage that happens routinely during intercourse even if you don’t feel it. Once inside, the bacteria trigger an immune response: your skin cells release signaling molecules that draw white blood cells to the area, creating inflammation. Within days, this process produces the painful, soft ulcers that define chancroid.
The infection can also spread through autoinoculation, meaning you can transfer it to other parts of your own body. If you touch an active ulcer and then touch another area of skin, particularly one with a small cut or abrasion, the bacteria can take hold there too. This is why avoiding contact with the infected area matters during an active outbreak. Pus from the ulcers is highly infectious, and transferring that fluid to the eyes, fingers, or other skin is a documented route of spread.
What Happens After Exposure
The incubation period is short, typically 3 to 7 days after exposure. The first sign is a small, painful bump on the genitals or surrounding skin. This bump quickly breaks open into a shallow ulcer with ragged, undermined edges, meaning the surrounding tissue hangs slightly over the wound’s border. The base of the ulcer often looks grayish or yellowish and bleeds easily when touched. Unlike a syphilis sore, which is firm and painless, chancroid ulcers are soft and notably painful.
Multiple ulcers can develop, and nearby lymph nodes in the groin often swell and become tender. In some cases, these swollen nodes form a large, painful abscess that may need to be drained.
Sexual vs. Non-Sexual Transmission
In the United States and other high-income countries, sexual contact is the primary transmission route. The CDC notes that finding chancroid ulcers on a child’s genital area is considered highly suspicious for sexual abuse, precisely because the infection so rarely spreads any other way in these settings.
The picture looks different in tropical regions, particularly countries where yaws (a related skin disease) is common. In those areas, H. ducreyi causes nonsexually transmitted skin ulcers, especially in children. These ulcers typically appear on the legs and arms rather than the genitals, spreading through direct skin contact with infected wounds in settings where minor cuts and insect bites are frequent and hygiene resources are limited.
Who Is Most at Risk
Your risk depends largely on geography and sexual behavior. Chancroid has become rare in the United States and Western Europe but remains more common in parts of Africa, the Caribbean, and Southeast Asia. Having multiple sexual partners, especially in areas where chancroid circulates, increases your exposure risk significantly.
People living with HIV face a compounded problem. Chancroid ulcers create open wounds on the genitals, which makes it easier for HIV to enter or exit the body. The two infections tend to reinforce each other: HIV weakens the immune response that would normally fight off H. ducreyi, and chancroid sores provide a direct pathway for HIV transmission between partners.
Uncircumcised men also appear to be at higher risk. The warm, moist environment under the foreskin may give the bacteria a more favorable surface for establishing infection, and the foreskin itself is more susceptible to the micro-tears that H. ducreyi needs to penetrate the skin.
How to Reduce Your Risk
Condoms provide meaningful protection because they create a physical barrier between your skin and an infected ulcer. However, condoms only cover the areas they contact. If an ulcer is located on skin that the condom doesn’t cover, such as the outer labia, the base of the penis, or the groin, transmission can still occur.
The most effective prevention involves limiting sexual contact with partners who have visible genital sores, particularly in regions where chancroid is endemic. If you notice an unfamiliar sore on a partner, postponing sexual contact until it has been evaluated is a practical step. And if you develop an ulcer yourself, avoiding both sexual contact and touching the sore reduces the risk of spreading it to partners or to other parts of your own body.
How Chancroid Is Diagnosed and Treated
Diagnosis can be tricky because the bacterium is difficult to grow in a standard lab culture, and no widely available rapid test exists for it. In practice, clinicians often diagnose chancroid based on the appearance of the ulcer combined with ruling out other causes of genital sores, particularly syphilis and herpes. If your ulcer is painful and soft (rather than firm and painless like syphilis), and tests for herpes and syphilis come back negative, chancroid becomes the likely diagnosis.
The good news is that chancroid responds well to antibiotics. Treatment is typically a single dose or a short course, and most people see improvement within a few days. Ulcers generally begin healing within a week, though larger sores can take two weeks or longer to fully close. Sexual partners from the 10 days before your symptoms appeared should also be treated, even if they have no visible sores, to prevent reinfection and further spread.