A patient walks into an urgent care clinic with a painful rash and a low-grade fever. The doctor considers chickenpox, herpes, an allergic reaction. Mpox doesn't make the list because the doctor hasn't seen a case and the patient doesn't fit the assumed demographic. That diagnostic blind spot has delayed treatment and enabled transmission in multiple outbreaks since 2022.
Knowing what mpox looks like, stage by stage, puts you ahead of many frontline clinicians. You won't diagnose yourself, but you'll know when to push for the right test instead of accepting the wrong answer.
What happens during the incubation period?
After exposure, mpox incubates for 5-21 days with an average of 6-13 days. During this window, you're infected but have no symptoms and are generally not considered contagious. Incubation length varies by route of transmission: direct contact with lesions tends to produce shorter periods of 5-7 days, while respiratory exposure may take longer. Sexual transmission during the 2022 Clade IIb outbreak showed a median incubation of about 7-8 days, based on a multinational study of 528 cases published in the New England Journal of Medicine.
If you've been notified of an exposure, monitor yourself daily for 21 days. Take your temperature each morning and check your skin, particularly your face, hands, genitals, and perianal area.
What does the prodrome feel like?
Before the rash appears, most patients experience 1-5 days of systemic symptoms: fever (often 38.5-40.5°C / 101-105°F), intense fatigue, muscle aches, and headache. One symptom stands out as a clinical differentiator. Lymphadenopathy, or swollen lymph nodes, occurs in the majority of mpox cases and is often the first noticeable sign.
Swollen nodes typically appear in the neck, armpits, or groin. They're tender to the touch and can swell to 1-4 cm. Chickenpox does not cause lymphadenopathy. Neither does herpes simplex in most cases. If you develop a fever with painful, swollen lymph nodes and a subsequent rash, mpox should be on the differential.
Some patients in the 2022 outbreak presented without a notable prodrome, moving directly to localized rashes, particularly in the genital or perianal region. Atypical presentations were common enough that the CDC updated its clinical guidance to warn against ruling out mpox based on the absence of systemic symptoms alone.
What are the rash stages?
Mpox rash progresses through five distinct stages over 2-4 weeks. Recognizing which stage you're looking at helps gauge how far along the infection is and how long isolation will last.
Macules appear first: flat, discolored spots on the skin, typically 2-5 mm in diameter. They're easy to mistake for bug bites or an allergic reaction at this stage. Macules usually emerge 1-3 days after the prodrome begins, often starting on the face before spreading to the trunk and extremities. In the 2022 outbreak, many cases presented with lesions concentrated on the genitals and perianal area rather than the face.
Papules develop within 1-2 days as the macules raise and harden into firm, rounded bumps. They feel solid to the touch, distinctly different from the fluid-filled blisters of chickenpox. Papules are often described as feeling like a BB pellet embedded under the skin.
Vesicles form next as the papules fill with clear fluid. Lesions become raised, tense, and dome-shaped, measuring 5-10 mm. They may be itchy or painful. At this stage, the rash can resemble chickenpox, but mpox vesicles are deeper-seated, firmer, and tend to be more uniform in size and stage across the body. Chickenpox lesions typically appear in successive "crops" at different stages simultaneously.
Pustules replace vesicles as the clear fluid turns opaque and yellowish. Pustules are the most recognizable stage, firm and round with a depressed center (umbilicated). They're highly infectious. Contact with pustule fluid is one of the primary transmission routes.
Crusts form as pustules dry over 5-7 days. Scabs darken, harden, and eventually fall off, leaving depigmented or pitted scars in some cases. A patient remains infectious until every crust has separated from the skin and new skin has formed underneath. That process takes 2-4 weeks from rash onset.
How does Clade IIb differ from Clade Ib?
Two clades of mpox are circulating globally, and they behave differently enough to warrant separate attention.
Clade IIb drove the 2022 global outbreak that produced over 87,000 confirmed cases across 110+ countries. Transmission was concentrated among men who have sex with men, primarily through sexual contact and close skin-to-skin contact. Case fatality was low, roughly 0.1-0.2%, with deaths occurring primarily among immunocompromised individuals. Most patients recovered fully within 2-4 weeks.
Clade Ib is a recombinant strain circulating primarily in the Democratic Republic of the Congo and neighboring countries. As detailed in the PandemicAlarm Clade Ib situation report, this strain carries a higher case fatality rate, estimated at 3-5% in affected regions, with particularly severe outcomes in children under 15. Transmission patterns are broader, including household contacts, healthcare settings, and sexual transmission. Clade Ib has prompted a renewed PHEIC declaration from WHO.
For clinical recognition purposes, both clades produce the same progression of rash stages. Clade Ib tends to cause more extensive lesion counts, more frequent complications (secondary bacterial infections, respiratory involvement), and longer illness duration.
When should you suspect mpox instead of something else?
Several conditions mimic mpox at different stages. Knowing the distinguishing features speeds up accurate identification.
Mpox vs. chickenpox. Chickenpox lesions appear in waves, so you'll see macules, vesicles, and crusts all at the same time on the same patient. Mpox lesions progress through stages roughly in sync. Chickenpox is superficial and itchy; mpox is deep-seated and often painful. Chickenpox does not produce significant lymphadenopathy. Age matters too. Chickenpox is increasingly rare in vaccinated populations; if you were vaccinated against varicella and develop a vesicular rash, mpox should be considered.
Mpox vs. herpes simplex. Genital herpes produces grouped vesicles on an erythematous base, usually confined to one anatomical site. Mpox lesions are more widely distributed, firmer, and accompanied by systemic symptoms. Herpes recurrences are typically brief (7-10 days); mpox lasts 2-4 weeks.
Mpox vs. syphilis. Secondary syphilis can produce a widespread papular rash, including on the palms and soles. Syphilis rash is typically painless and not vesicular. A syphilis screen (RPR or VDRL) rules it out quickly.
When in doubt, ask for a test. You have the right to request it even if your clinician hasn't considered mpox.
How is mpox confirmed?
PCR testing of a lesion swab is the standard diagnostic method. A clinician unroofs a vesicle or pustule, swabs the base and fluid, and sends the sample to a public health or commercial laboratory. Results typically return within 24-72 hours. PCR sensitivity for lesion swabs exceeds 95% when samples are collected properly.
Blood PCR is less reliable for diagnosis and is not recommended as a primary test. If you suspect mpox, contact your local health department for the fastest testing route in your area.
Can vaccination help after exposure?
Yes, if you act fast. The Jynneos (MVA-BN) vaccine is a two-dose regimen approved for mpox prevention. When administered within 4 days of known exposure, it can prevent infection entirely. Given between days 4-14 post-exposure, it may not prevent infection but can reduce symptom severity.
Each dose is 0.5 mL injected subcutaneously. The second dose follows 28 days after the first. Full immunity develops approximately 2 weeks after the second dose. Single-dose effectiveness was estimated at 36-86% during the 2022 outbreak, depending on the study and population. Two doses brought effectiveness above 85%.
Jynneos is well-tolerated. Common side effects include injection site pain (85% of recipients), redness, and mild fatigue. Serious adverse events are rare. The vaccine is derived from Modified Vaccinia Ankara and does not contain replicating virus, making it safe for immunocompromised individuals.
When can you end isolation?
Isolation continues until all lesions have crusted over, the crusts have fallen off, and fresh skin has formed underneath. For most patients, this takes 2-4 weeks from rash onset. WHO and CDC guidelines are explicit: the presence of any remaining crust means you're still potentially infectious.
During isolation, cover lesions with clothing or bandages when you must share living space. Avoid sharing bedding, towels, and clothing. Wash contaminated linens in hot water with standard detergent. Mpox virus can survive on porous surfaces (fabric, bedding) for days to weeks, so laundering matters.
Monitor the PandemicAlarm map for current mpox activity in your region and review your area's reporting requirements. Many jurisdictions require healthcare providers to report confirmed mpox cases to public health authorities within 24 hours.