LymeHQ · Visual Reference

Rash identification

A rash is the one piece of evidence that can diagnose Lyme on its own — and the classic bull's-eye is the minority presentation, not the typical one. Nine rashes, how urgent each is, and how to tell them apart.

Read First

These are illustrations, not photographs, and real rashes vary enormously. Appearance differs between people and changes over days — and notably, these rashes can look very different on darker skin, where they are more often missed or diagnosed late. Use this page to know what to raise with a clinician. Never use it to rule something out. If a rash is growing, or you feel unwell, be seen.
Review statePending clinical review

Nine rash presentations, their urgency ordering, and the illustrations — 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.

The three things most people get wrong

Almost every delayed Lyme diagnosis involves at least one of these.

The bull's-eye is the exception. Most erythema migrans rashes are a uniform expanding red patch with no rings at all. Waiting for a target shape is one of the most common reasons treatment starts late.
Expansion is the diagnosis, not the shape. A mark that grows over a day or two is the signal. A mark that stays the same size or shrinks is almost always an ordinary reaction to the bite.
A spotted rash on wrists and ankles with fever is an emergency. That pattern suggests Rocky Mountain spotted fever, which worsens over days and is treated on suspicion rather than on a test result.
Get Urgent Care Guidance

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 most recognized Lyme rash — but present in only ~20% of EM cases. Concentric red rings with central clearing. Diagnostic for Lyme disease on clinical presentation alone — no positive test required to begin treatment.

    Appears
    3–30 days after bite · Average 7 days
    Size
    Expands to 5–30cm (2–12 in) over days
    Feel
    Usually painless · May be warm · Rarely itchy
    Location
    Anywhere · Common: thigh, groin, armpit, trunk
  • UrgentLyme Disease

    Atypical Erythema Migrans — (Uniform Red EM — Most Common)

    Borrelia burgdorferi infection

    This is the most commonly misdiagnosed Lyme rash — and the most common EM presentation in the US. A solid, uniformly red expanding oval with no bull's-eye pattern. Frequently dismissed as 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
  • 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 — more serious, but still highly treatable.

    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
  • 🚨 EmergencyRMSF · Rickettsia

    Rocky Mountain Spotted Fever — Petechial Rash — Medical Emergency

    Rickettsia rickettsii · American Dog Tick, Rocky Mountain Wood Tick

    This is a medical emergency. Fatal in 5–10% of treated cases, up to 80% if untreated. Tiny red/purple dots (petechiae) starting at wrists and ankles, spreading inward to the trunk. Accompanied by high fever (102–104°F) and severe headache.

    Pattern
    Wrists + ankles → spreads to trunk and face
    Appearance
    Tiny red/purple flat dots · non-blanching
    With
    High fever + severe headache always present
    Timing
    2–14 days after bite · rash may appear after fever
  • PromptSTARI · Lone Star Tick

    STARI Rash — (Southern Tick-Associated Rash Illness)

    Unclear pathogen · Lone Star tick (Amblyomma americanum)

    Visually identical to Lyme EM rash — expanding bull's-eye pattern — but caused by the Lone Star tick, not the deer tick. Standard Lyme tests will be negative. Treated similarly with doxycycline. Common in Southeast and South-Central US.

    Appearance
    Identical to Lyme EM — expanding bull's-eye
    Lyme Test
    NEGATIVE — standard test won't detect STARI
    Geography
    Southeast, South-Central US · Expanding north
    Treatment
    Doxycycline — same as Lyme
  • PromptBartonella Coinfection

    Bartonella Skin Manifestations — (Striae · Linear Streaks)

    Bartonella henselae / quintana / other spp.

    Bartonella causes distinctive linear reddish-purple streaks that resemble stretch marks — on the trunk, thighs, arms, and back. Often dismissed as normal striae. Combined with anxiety, rage episodes, and foot pain, these streaks are highly indicative of Bartonella.

    Appearance
    Linear reddish/purple streaks · stretch-mark like
    Location
    Trunk, thighs, arms, back · follow skin lines
    Key Context
    Often with anxiety, rage, foot pain, brain fog
    Standard Test
    Standard IFA only 28% sensitive — Galaxy FISH needed
  • 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 2–6 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 · 2–6hr delay
    Appearance
    Raised wheals (hives) · intensely itchy · widespread
    Severity
    Hives to anaphylaxis — carry epinephrine
    Test
    Blood test: Alpha-gal IgE — available at most labs
  • 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
  • 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 expand beyond 1–3cm and fades within days. This is a normal immune response to tick saliva — not a sign of Lyme disease or any tick-borne infection. The critical distinction: it does not grow.

    Size
    Small · under 5cm · does NOT expand over days
    Duration
    Fades within 1–3 days after tick removal
    Treatment
    None needed · monitor for expansion
    Watch for
    If it starts growing after 24–48h → see a provider

Side by side

The fastest way to separate an expanding rash that needs treatment from one that does not.

Tick-borne rashes compared by urgency, appearance, whether they expand, and whether they hurt
Rash / conditionUrgencyKey appearanceExpanding?Painful?
Classic Erythema MigransUrgent3–30 days after bite · Average 7 daysExpands to 5–30cm (2–12 in) over daysUsually painless · May be warm · Rarely itchy
Atypical Erythema MigransUrgentSolid red · uniform color · no central clearing—Warm to touch · usually not painful or itchy
Multiple Erythema MigransUrgentDays to weeks after primary rash——
Rocky Mountain Spotted Fever🚨 EmergencyTiny red/purple flat dots · non-blanching——
STARI RashPromptIdentical to Lyme EM — expanding bull's-eye——
Bartonella Skin ManifestationsPromptLinear reddish/purple streaks · stretch-mark like——
Alpha-gal Urticaria / HivesUrgent if severeRaised wheals (hives) · intensely itchy · widespread——
CellulitisUrgent — treat separately———
Tick Bite IrritationMonitor OnlySmall · under 5cm · does NOT expand over daysSmall · under 5cm · does NOT expand over days—

What to do now

Photograph it today, with the date and something for scale. A coin or a ruler beside the rash is enough. Rashes fade, and a dated series showing growth is often more persuasive to a clinician than the rash itself weeks later.
Draw around the edge with a pen. The single most useful thing you can do at home: if the rash has visibly outgrown the line within a day, that is expansion, and expansion is what matters.
A negative test does not clear an expanding rash. Antibodies take weeks to appear, so early testing is often negative in genuine infection. Why the timing matters

Want us to remind you to check?

No rash yet — just a bite? The window when one would appear is longer than anyone naturally keeps checking. We’ll email you three times — around day 7, day 14 and day 30 after today — because that brackets the window when a rash would actually appear. No account, nothing to install.

Reminders are not switched on in this build yet — the sending half is not configured, so nothing here collects an address until it is.

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