UV & Skin Log

Track sun exposure and skin reactions to spot your triggers

Local UV index

Date

Start End

Leave times blank to use the whole day. Pick a past or future date to see the peak for that day.

Enter UV index manually

Log a day

Record today's exposure & symptoms

The more consistently you log, the clearer your triggers become.

Date Activity

Clothing UV index

Direct sun (min) Indirect / shade (min)

Symptom Sensation

Body location Severity

Notes

History

Logged days

Three conditions, three different causes

They can look similar, but they start in completely different ways. The cause is what tells them apart — and what changes how you prevent each one.

Heat rash (miliaria / prickly heat)

Cause: trapped sweat — not sunlight

Mechanism: Sweat ducts get blocked, so sweat is trapped under the skin and leaks into surrounding tissue, causing irritation. UV plays no role.
Triggers: Heat, humidity, heavy sweating, tight or occlusive clothing, friction, fever, being unable to cool down.
Looks like: Clusters of tiny bumps or pinhead clear blisters; a prickly or stinging feeling.
Where: Covered, sweaty, friction-prone areas — back, chest, skin folds, waistband and bra lines, neck.
Timing: During or right after getting hot and sweaty; eases once the skin cools and dries.

Polymorphic light eruption (PMLE)

Cause: UV radiation — an immune reaction to light

Mechanism: An abnormal, delayed immune reaction to UV (mainly UVA, some UVB). The body reacts to sun-altered skin as if it were foreign. Sweat is not the cause.
Triggers: Sun exposure after a gap — classically the first strong sun of spring, a sunny holiday, or even UVA through window glass.
Looks like: Itchy red papules, small blisters, or raised plaques. "Polymorphic" = varies between people, but tends to be the same pattern each time for one person.
Where: Intermittently exposed skin — the V of the chest, outer arms, forearms, neck. Often spares the face and backs of hands, which are used to daily sun.
Timing: Hours to a couple of days after exposure; settles over days to ~2 weeks, often improving as the season goes on ("hardening").

Sunburn

Cause: UV radiation — direct skin damage

Mechanism: UV (mainly UVB) directly damages skin-cell DNA, triggering inflammation. It's dose-dependent: more UV and more time means more burn.
Triggers: Unprotected time in strong sun; higher UV index, reflective surfaces (water, snow, sand), altitude, missed or worn-off sunscreen.
Looks like: Flat, diffuse redness that's warm and tender; in worse cases swelling, blisters, then peeling. Sore rather than bumpy or itchy.
Where: Skin that was directly exposed, usually with sharp borders at clothing, strap, or sunscreen lines.
Timing: Redness starts ~2–6 hours after exposure and peaks around 12–24 hours.

Note: This library is for general education and consultation prep. It can't diagnose you, and other photosensitive conditions (for example a lupus-related rash, solar urticaria, or a drug reaction) can mimic these. Use it to describe what you see more precisely to a clinician.

Side by side

Quick distinguishing table

The fastest tells are sensation, where it appears, and its relationship to heat vs light.

	Heat rash	PMLE	Sunburn
Root cause	Trapped sweat	Immune reaction to UV	Direct UV damage
Feels	Prickly, stinging	Itchy	Sore, tender
Looks	Tiny bumps / clear blisters	Itchy papules / plaques	Diffuse flat redness
Where	Covered, sweaty folds	Intermittently sun-exposed (chest, arms)	Directly exposed, sharp lines
Onset	While hot & sweaty	Hours–days after sun	2–6 h after sun
Linked to	Heat & humidity	Light (even through glass)	UV dose & time
Eases when	You cool down	You avoid sun (days–weeks)	Skin heals (days)

Guided check

Which pattern fits best?

Answer for your current/most recent reaction. This sorts your description toward the closest pattern to discuss — it is not a diagnosis.

Closest patterns to your description

See a clinician promptly if you notice…

Fever, feeling unwell, dizziness, nausea, or confusion alongside the rash
Widespread blistering, raw or weeping skin, or rapid spreading
Signs of infection — increasing pain, warmth, swelling, pus, or red streaks
A rash that keeps recurring, scars, or doesn't settle as expected
A persistent rash across the cheeks/nose, or one with joint pain or marked light sensitivity

Appointment prep

Bring this to your consultation

Dermatologists diagnose photosensitive rashes largely from the story and timing. Have these ready:

Dated photos of the rash at its worst and as it fades
How long after sun/heat it appeared, and how long it lasted
Exactly where on the body (and whether face/hands were spared)
Sensation: prickly vs itchy vs sore
What you were doing, wearing, and the UV index that day (your log covers this)
Whether it followed direct sun, shade, or even sun through glass
Seasonality — does it flare with the first strong sun each year?
Sunscreens, medications, and supplements you use

Not medical advice. This tool supports self-tracking and helps you prepare for a professional consultation. It does not diagnose conditions or replace a clinician. If you're worried about a rash — especially with the warning signs above — please seek medical care.