The erythema migrans rash is the one Lyme finding clinicians act on by sight — an expanding red patch at or near the bite, usually days to a few weeks later, often warm, rarely itchy, sometimes with a paler ring. It is not always a bull's-eye. A Johns Hopkins study (JAMA Network Open, 12 December 2023) found that Black patients were less likely than white patients to be diagnosed while the rash was the only sign, and the researchers point partly to how the rash looks on darker skin (Johns Hopkins Medicine news release, December 2023, read 7 October 2026). Photograph it beside a coin today and again tomorrow; growth over days is the tell. The rash is a reason to see a clinician promptly, not a diagnosis you make at home.
Bites of many insects leave a small red welt. The Lyme rash is later, larger, and grows. A reaction within hours is almost never it.
- 1 · Within hours
A small mark at the bite, sometimes itchy. It stays small and fades within days.
Mark its edge with a pen and watch it.
- 2 · Days to weeks after the bite
The rash: “Begins at the site of a tick bite after a delay of 3 to 30 days (average is about 7 days)”
Source: CDC, Signs and Symptoms of Untreated Lyme Disease (opens in a new tab), read 10 October 2026. A red patch that expands over days — usually painless, may be warm. A ring is the minority.
See a clinician.
- 3 · Days to weeks after the first rash
More patches at sites away from the bite — the infection has spread.
See a clinician the same day.
What most people get wrong
The emergency pattern is at the top of the page. These two are what delay most Lyme diagnoses.
The nine rashes
Ordered by urgency. Each entry opens to what to look for, why it gets missed, and what to do — expand only what you need.
- UrgentLyme Disease
Classic Erythema Migrans — (Bull's-Eye EM Rash)
Borrelia burgdorferi infection
The rash everyone pictures — and the minority of them. Concentric red rings with central clearing. Diagnostic for Lyme disease on clinical presentation alone — no positive test required to begin treatment.
- Size
- Expands over days — the growth is the finding, not the measurement
- Feel
- Usually painless · May be warm · Rarely itchy
- Location
- Anywhere · Common: thigh, groin, armpit, trunk
The rash: “Begins at the site of a tick bite after a delay of 3 to 30 days (average is about 7 days)”
Source: CDC, Signs and Symptoms of Untreated Lyme Disease (opens in a new tab), read 10 October 2026. Full clinical detail
What to look for
- Expanding rash — if it's growing, this is the most important sign
- Central clearing creates concentric rings (the "target")
- May not appear at the bite site — can show up elsewhere on body
- May be visible but not felt — check your skin after outdoor activity
What to do
- Contact a provider today. An expanding rash of this kind is diagnostic for Lyme on its own — clinicians treat it without waiting for a blood test, which is often negative this early.
- Photograph it now, with something for scale and the date. The rash fades, and a dated photo may be the strongest evidence you have later.
- The antibiotics most often used are doxycycline, amoxicillin and cefuroxime. Which drug, how much and for how long are your provider’s decisions, and whether a medicine suits a child is the prescriber’s decision.
- Ask what should happen if symptoms persist after the course finishes, before you leave the appointment.
Key facts
- CDC reports the expanding rash in roughly 70 to 80 percent of people with Lyme disease — so some people never get one — and it is not always a bull’s-eye (Signs and Symptoms of Untreated Lyme Disease, read 25 September 2026). The ringed bull’s-eye is the smaller share of those rashes.
- In the US, uniform red expansion is more common than concentric rings
- Surveillance case definitions use a minimum size, but that is a rule for counting cases rather than a rule for treating one — a smaller rash that is growing still fits the picture
- UrgentLyme Disease
Atypical Erythema Migrans — (Uniform Red EM — Most Common)
Borrelia burgdorferi infection
The EM rash without a bull's-eye — a solid, uniformly red expanding oval. Because it does not match the picture most people have, it can be mistaken for a spider bite, heat rash or contact dermatitis.
- Appearance
- Solid red · uniform color · no central clearing
- Key Feature
- EXPANDS over days — the expansion is the diagnosis
- Border
- May be irregular or slightly raised
- Feel
- Warm to touch · usually not painful or itchy
Full clinical detail
Why this gets missed
- Looks nothing like the textbook bull's-eye most doctors are taught to recognize
- It can be mistaken for a spider bite, ringworm or contact dermatitis
- Say you have been around ticks — without that, the rash can be read as something else
The one question to ask
- "Is it getting bigger?" — If yes, it's EM until proven otherwise
- Take a photo with your thumb next to it today, same tomorrow — compare
- Mark the border with a fine-tip marker and see if it expands outside the mark
Treatment — same as classic EM
- Treated exactly as a classic bull’s-eye rash. The uniform appearance does not mean a milder infection — it is simply the more common presentation.
- Clinicians diagnose an EM rash on sight and treat it without waiting for a blood test, because testing this early is often negative in genuine infection.
- Your provider selects the antibiotic and the course, and whether a medicine suits a child is the prescriber’s decision.
- UrgentLyme — Disseminated
Multiple Erythema Migrans — (Disseminated Lyme Disease)
Borrelia burgdorferi — systemic dissemination
Multiple EM rashes appearing at sites away from the original bite indicate the bacteria has entered the bloodstream and is disseminating through the body. This is early disseminated Lyme, and a reason to be seen promptly.
- Appears
- Days to weeks after primary rash
- Number
- 2 to dozens — vary in size
- Meaning
- Systemic dissemination — bacteria in bloodstream
- Urgency
- Same-day treatment — may need IV antibiotics
Full clinical detail
What this means clinically
- Bacteria has disseminated hematogenously — it's in the bloodstream
- Secondary rashes are NOT from new tick bites — they're the same infection spreading
- Higher risk of cardiac, neurological, and joint complications
Additional symptoms to watch
- Shooting pains, numbness or tingling — Lyme neuropathy. Worth reporting at the appointment rather than waiting to see whether it settles.
- The box headed “Symptoms that mean go now, not tomorrow”, on the card itself, holds the ones assessed the same day. These are the ones to write down and bring with you.
Treatment at this stage
- Multiple lesions mean the infection has disseminated through the bloodstream. This is treated more assertively than a single rash and should be assessed the same day.
- Tell the provider how many lesions there are and when each appeared. Dissemination changes what they consider, including whether intravenous treatment is warranted.
- How long treatment runs at this stage is for the clinician treating you to decide with you. Ask what they intend, and why, rather than assume.
- Ask whether coinfection testing is warranted. A tick that transmitted enough Borrelia to disseminate may have carried more than one organism.
- 🚨 EmergencyRMSF · Rickettsia
Rocky Mountain Spotted Fever — Petechial Rash — Medical Emergency
Rickettsia rickettsii · American Dog Tick, Rocky Mountain Wood Tick
This is a medical emergency. Tiny red/purple dots (petechiae) starting at wrists and ankles and spreading inward to the trunk. The illness usually begins with a sudden fever and headache, and the rash often comes days later or not at all early on. It worsens over days and is treated on suspicion rather than on a test result — delay is what makes it dangerous.
- Pattern
- Wrists + ankles → spreads to trunk and face
- Appearance
- Tiny red/purple flat dots · non-blanching
- With
- Usually a sudden fever and headache — not every case has both at first
Full clinical detail
Emergency treatment
- Doxycycline is the recommended treatment for adults and children of all ages (CDC). Clinicians start it when they suspect RMSF rather than waiting for a test, because the test takes longer than the illness allows.
- If you are ill after a tick bite, or after time where ticks live, be seen the same day and say you have been around ticks.
Critical facts
- Despite the name, cases occur throughout the United States; most are reported from Arkansas, Missouri, North Carolina, Oklahoma and Tennessee
- The rash may be absent or late. Fever and headache after a tick bite are reason to be seen promptly — clinicians treat on suspicion rather than waiting for the rash or a test
- Carried by American Dog Tick (Dermacentor variabilis) — common throughout the US
- PromptSTARI · Lone Star Tick
STARI Rash — (Southern Tick-Associated Rash Illness)
Unclear pathogen · Lone Star tick (Amblyomma americanum)
Can look just like a Lyme EM rash — an expanding red patch, sometimes a bull's-eye — but it is associated with the Lone Star tick, not the deer tick. Its cause is not known and there is no blood test for it. A Lyme test cannot separate the two early: it is often negative in the first weeks of real Lyme too, so a negative early test is never a sign that the rash is STARI. It is not known whether antibiotics help, and what to do about the rash is a clinician's judgement. Reported mainly in the Southeast and South-Central US.
- Appearance
- Identical to Lyme EM — expanding bull's-eye
- Lyme Test
- Cannot separate them early — often negative in early Lyme too
- Geography
- Southeast, South-Central US · Expanding north
- Treatment
- No established regimen — a clinician's judgement
Full clinical detail
Why this matters
- An early negative Lyme test does not rule Lyme out, whichever tick bit you — antibodies take several weeks to appear, and an EM rash is diagnosed by sight
- There is no test for STARI. It is not known whether antibiotics help it; because it resembles early Lyme, some clinicians treat it
- The Lone Star tick is expanding its range northward — STARI cases are increasing outside the traditional South
How to identify the tick
- Lone Star tick has a single white dot on the female's back — distinctive
- Deer tick (Lyme vector) is smaller and all dark — no white dot
- If you saved the tick, bring it or a clear photo — which tick bit you is part of how a clinician tells these rashes apart
What to tell your doctor
- Describe it plainly: an expanding rash, when it appeared, and a Lone Star tick bite — then ask what they would do about the rash itself, given that a Lyme test would not settle it either way.
- STARI has no identified cause and no trial evidence that antibiotics change its course. A clinician may still decide to treat, and that is a judgement rather than a guideline you can hold them to.
- PromptNot established as tick-borne
Bartonella Skin Streaks — (Case-Report Descriptions · Not a Tick Rash)
Bartonella henselae / quintana / other spp.
Linear reddish-purple streaks resembling stretch marks have been described in case reports of Bartonella infection. They are not a validated sign — nothing about a streak tells you what caused it — and this is not a tick rash. CDC states there is no evidence that ticks spread Bartonella to people. It is here because people who have read about it ask.
- Appearance
- Linear reddish/purple streaks · stretch-mark like
- Location
- Described on the trunk, thighs, arms and back
- How it is spread
- Fleas, body lice, sand flies, cat scratches — not established for ticks
- Standard Test
- Serology has known limits — a negative does not settle it
Full clinical detail
What is and is not established
- Bartonella is spread to people mainly by fleas, body lice and sand flies, and by scratches from flea-infested cats.
- CDC states there is no evidence that ticks spread Bartonella to people.
- It has been found in ticks, and one laboratory study showed a tick passing it to an animal; whether that happens in nature is not known. Some clinicians who treat persistent illness after a tick bite consider it anyway — a proposed route of infection, not an established one.
- The streaks come from case reports rather than studies, so they are not a way to tell Bartonella from anything else. A contact with cats, fleas or lice is the more useful thing to mention.
Testing
- Standard Bartonella serology has known limits, which makes a negative result weaker evidence here than a negative Lyme test is
- Specialty laboratories run Bartonella-specific panels a conventional lab does not, usually out of pocket. This page cannot rank their accuracy for you — ask which assay was used and how it was validated, and take that answer to whoever is treating you.
Treatment
- Bartonella infections are treated with antibiotics, and which ones is a prescribing decision. Tell your prescriber everything else you take — some of the drugs used change how other medicines are broken down.
- Urgent if severeAlpha-gal Syndrome
Alpha-gal Urticaria / Hives — (Lone Star Tick Allergy · Delayed Meat Reaction)
IgE-mediated allergic reaction to galactose-alpha-1,3-galactose · Lone Star tick sensitization
Raised, intensely itchy hives appearing hours after eating red meat or mammalian products. The delay is the diagnostic key — most food allergies appear immediately. Caused by Lone Star tick bite sensitizing the immune system to the alpha-gal sugar found in mammalian products.
- Trigger
- Red meat · dairy · mammalian gelatin
- Appearance
- Raised wheals (hives) · intensely itchy · widespread
- Severity
- Hives to anaphylaxis — carry epinephrine
- Test
- Blood test: Alpha-gal IgE — available at most labs
Full clinical detail
The delayed reaction pattern
- Reaction starts hours after eating red meat — not immediately like most food allergies
- This delay causes patients and doctors to miss the connection to meat
- Exercise after eating can intensify the reaction — "cofactor-augmented anaphylaxis"
- Fatty cuts of meat tend to trigger stronger reactions than lean cuts
What to do
- Ask about being prescribed an adrenaline (epinephrine) auto-injector, and make sure the people you eat with know where you keep it.
- Strict avoidance of red meat and mammalian products — including pork, lamb and venison, and for some people dairy and mammalian gelatin.
- Ask about an alpha-gal IgE blood test. Poultry and fish do not contain alpha-gal.
Rising prevalence
- Alpha-gal cases have surged with expanding Lone Star tick range
- CDC has described alpha-gal syndrome as under-recognised — many people are sensitized and never diagnosed
- Many cases go undiagnosed — the delayed reaction pattern leads to years of mystery symptoms
- Urgent — treat separatelyLyme Look-alike
Cellulitis — (Common EM Misdiagnosis — Bacterial Skin Infection)
Staphylococcus aureus / Streptococcus pyogenes · not tick-borne
The most common misdiagnosis for atypical EM rash. Cellulitis is a bacterial skin infection — not Lyme disease — but looks similar to a solid red expanding rash. The key differences: cellulitis is painful and tender to the touch, feels hot, and often has a clear skin-break origin point.
- vs. EM
- PAINFUL (EM is usually painless) · HOT to touch
- Origin
- Often from skin break · wound · insect bite
- Danger sign
- Red streaks spreading = lymphangitis — urgent
- Treatment
- Oral antibiotics (different from Lyme tx) · not doxy
Full clinical detail
How to tell it's cellulitis, not EM
- Pain on touch — EM is typically painless. Cellulitis hurts when you press it.
- Heat — cellulitis is noticeably hot to the touch. EM may be warm but not significantly.
- Cellulitis often has a clear entry point (cut, insect bite, wound) near the center
- Cellulitis has an ill-defined border that spreads outward without the organized ring structure
Treatment
- Treated with antibiotics; which one is the prescriber's decision, based on the bacteria likely to be involved
- Rest, elevation of the affected limb, warm compresses
- Monitor OnlyNot Infectious
Tick Bite Irritation — (Local Reaction — Not Infection)
Local immune/allergic response · not a tick-borne pathogen
A small red area at the tick bite site that does not grow and fades over the days that follow. This is a normal immune response to tick saliva — not a sign of Lyme disease or any tick-borne infection. The distinction that matters is not how big it is: it is whether it gets bigger.
- Size
- Small and unchanging · does NOT grow past a marked border
- Duration
- Fades after tick removal
- Treatment
- None needed · monitor for expansion
- Watch for
- If it starts growing → see a provider
Full clinical detail
How to monitor correctly
- Mark the border of the redness with a fine-tip marker immediately after tick removal
- Check again — if redness stays within or fades: normal reaction
- If redness expands OUTSIDE the marked border → this may be EM → see a provider
Is preventive treatment worth asking about?
- A preventive antibiotic after a high-risk bite is offered in some circumstances. Whether you qualify depends on the tick species, how long it was attached, how common Lyme is where you were bitten, and how recently it was removed.
- Whether to offer it is the clinician’s judgement on those facts. Ask directly rather than assuming you were considered and declined.
- It is time-sensitive, so ask as soon as you can after the tick is out rather than waiting to see whether symptoms develop. Your provider knows what window they are working to; this page does not set one.
- Submitting the tick for species identification and pathogen testing gives your provider information that informs this decision.
What does NOT need treatment
- Redness that stays the same size or shrinks — local reaction
- Slight itching or mild swelling directly at the bite site — normal
Side by side
The fastest way to separate an expanding rash that needs treatment from one that does not.
| Rash / condition | Urgency | Key appearance | Expanding? | Painful? |
|---|---|---|---|---|
| Classic Erythema Migrans | Urgent | Red patch with central clearing — concentric rings | Yes — grows over days | Usually painless, often warm |
| Atypical Erythema Migrans | Urgent | Solid, uniformly red oval — no rings | Yes — the expansion is the finding | Usually painless, often warm |
| Multiple Erythema Migrans | Urgent | Several patches, including away from the bite | Yes — each patch grows | Usually painless |
| Rocky Mountain Spotted Fever | 🚨 Emergency | Tiny flat red/purple dots, wrists and ankles first | Spreads inward over days, dot by dot | Not typically — fever and severe headache dominate |
| STARI Rash | Prompt | Looks like EM, after a Lone Star tick bite | Yes — indistinguishable from EM by sight | Usually painless |
| Bartonella Skin Streaks | Prompt | Linear reddish-purple streaks, like stretch marks | No — streaks appear and fade rather than spread outward | Not usually |
| Alpha-gal Urticaria / Hives | Urgent if severe | Raised weals (hives), often widespread | No — hives come and go, hours after eating | Intensely itchy rather than painful |
| Cellulitis | Urgent — treat separately | Solid red area, often from a break in the skin | Yes — spreads with an ill-defined edge | Yes — painful to press and hot to touch |
| Tick Bite Irritation | Monitor Only | Small mark at the bite itself | No — stays inside a marked border | Mildly itchy at most |
What this table cannot separate. On the day it appears, early erythema migrans, a STARI rash and early cellulitis can look the same, and a single photograph of any of them can look like the others. Every row describes how that rash typically behaves, not how yours will. What tells them apart is change — whether it grows past a pen line, whether it hurts, what else you feel — and even then it is a clinician looking at it who settles it, not this page.
How often the rash is missed in real practice, when it is there. That would need a study of people who were not already in a clinic, and we have not found one.
- This appeared on this date after this exposure — would you treat on sight?
Review statePending clinical review
Nine rash presentations, their urgency ordering, the notes that used to be painted into the illustrations (now text under each card, each flagged), and the illustrations themselves — which render one complexion, as the note on the page says. A clinically-informed reviewer has not yet signed this off, and it stays marked until one does.