It is medical ultraviolet light.
Controlled UV exposure treats selected inflammatory skin diseases.
Phototherapy vs Punch Biopsy
Phototherapy: A prescribed medical light treatment that uses a narrow band of ultraviolet B, usually two or three times a week, to calm psoriasis and eczema and to bring color back in vitiligo. A tanning bed is a different thing and is not a substitute.
Punch Biopsy: A small round blade takes a full-thickness core of skin, usually 3 or 4 millimeters across, closed with a stitch or two. It is the standard biopsy for rashes and for anything where the deeper layers matter.
Choose Phototherapy if…
Choose for widespread psoriasis, eczema or vitiligo when creams can't cover enough skin and you can attend 2–3 times a week.
- Too much skin to treat with creams
- You'd prefer to avoid pills or injections
- The clinic is close enough for frequent visits
Choose Punch Biopsy if…
Choose when a rash or growth needs a definite diagnosis that looking alone can't give.
- An unclear or stubborn rash
- A growth that might be cancer
- The deeper skin layers matter
Alternatives, not combined
Can you have both?
They serve different purposes. A biopsy confirms the diagnosis; phototherapy treats conditions like psoriasis or eczema.
Key differences
● Phototherapy
● Punch Biopsy
DowntimeNone → 2+ weeks
None
1–2 weeks
PainMinimal → Needs anesthesia or sedation
Minimal
Mild
Results showImmediately → 3+ months
1–3 months
1–4 weeks
How long it lastsWeeks → Years or permanent
6–12 months
Years or permanent
Visits neededOne → Every few months
A longer series (4–6+)
One
Cost per visit$ → $$$$$
$
$
ReversibleYes, can be undone → No, permanent
No, fades slowly
No, permanent
What is it?
Phototherapy
Punch Biopsy
What is it?
Narrowband UVB is most common.
PUVA combines a light-sensitizing medicine with UVA.
Tanning beds are not a substitute.
They are not equivalent to medical phototherapy.
History is reviewed.
Medicines, skin cancer history and cumulative exposure are checked.
It samples a cylinder of skin.
A circular blade removes a small core of tissue.
It reaches deeper layers.
It samples the epidermis, dermis and sometimes fat.
It investigates rashes and lesions.
It is a diagnostic procedure.
Melanoma needs a specific plan.
A partial sample may not characterize a whole mole.
What it treats
Evidence level
Phototherapy
Punch Biopsy
Strong evidenceMost established uses
Psoriasis
Clears widespread plaques.
Eczema
Reduces itch and rash.
Vitiligo
Restores color.
Suspicious Growths
Confirms a diagnosis.
Moderate evidenceSome supportive research
—
Psoriasis
Confirms an unclear rash.
Not effective
—
Acne
Not needed for diagnosis.
Can make it worse
Melasma
UV light darkens patches.
Rosacea
Light triggers flushing.
—
Treatment areas
Treatment areas
Affected skin may be treated in a whole-body booth or with a smaller unit; unaffected areas may be shielded.
The specific lesion, scar or affected patch determines the treatment site; there is no fixed body distribution.
Skin tones
Skin tone
● Phototherapy
● Punch Biopsy
Lighter skin
Some risk
Burns more easily; lower starting doses.
Low risk
A tiny scar.
Medium skin
Low risk
Tanning of untreated skin.
Low risk
A tiny scar.
Deeper skin
Low risk
Tans darker; vitiligo edges may stand out at first.
Some risk
Small raised or dark scar possible.
How it works
Phototherapy
Punch Biopsy
How it works
Diagram explanation
Measured UV light reaches skin: A clinician selects and monitors the light exposure. Inflammatory activity changes: UV treatment can reduce overactive immune activity in skin. Skin symptoms may improve: Repeated treatment can help selected inflammatory conditions.
Schematic illustration. Technique and response vary. This explains a mechanism and does not specify treatment settings.
A site is selected and numbed: The clinician chooses an informative area to sample. A small skin core is taken: A circular blade samples epidermis and dermis. The laboratory examines it: The sample helps establish a diagnosis; the wound is cared for.
Schematic illustration. Technique and response vary. This explains a mechanism and does not specify treatment settings.
Before your treatment
Phototherapy
Punch Biopsy
2–4 weeks before
Not specified
1 to 2 weeks before: Steroid cream: Stop the steroid cream a week or two before if you can.
The week before
Between sessions: Sun and tanning: No sunbathing, no tanning beds.
Not specified
Day of treatment
Phototherapy
Punch Biopsy
Before you arrive
Clean skin: Emollient on plaques only if told to.
Goggles and shielding: Know which areas will be shielded, and bring your own goggles if you have them.
Eating and clothes: On the scalp a small patch is trimmed short, not shaved bald.
Eating and clothes: Eat normally, take your usual medicines, wear clothes that make the site easy to reach.
Arrival & prep
You are asked whether your skin burned, stung or went pink after the last session.
The site is chosen, and not always the one you would pick — for a rash, usually fresh untreated skin rather than the oldest patch.
Treatment
You undress to the treated areas, put on goggles, and step into the cabinet.
Men get genital shielding — standard, not optional. The face is covered if it is not affected. Lamps run from a few seconds early in a course to several minutes later. You stand still and turn if asked. It does not hurt, and most people feel only warmth.
The skin is cleaned and stretched so the hole closes as a line, not a circle.
The punch is pressed and rotated, the core lifted out and cut free, then pressure stops the bleeding. One or two stitches and a dressing follow. You feel firm pressure and twisting, nothing sharp — say so if you do, and more anesthetic goes in.
Before you leave
Skin may look slightly pink and feel warm, like light sun.
A dressing for 24 hours, aftercare instructions, a stitch removal date, and a plan for how the result reaches you.
After your treatment
Phototherapy
Punch Biopsy
First 24 hours
Days 1 to 2: A faint pink that fades by the next day is expected, and it is how the dose is judged.
Days 1 to 3: From day two, wash with soap and water once a day, pat dry, apply plain petroleum jelly and re-cover.
Days 2–7
Not specified
Days 5 to 14: Face stitches come out at about 5 to 7 days, elsewhere at 10 to 14.
Weeks 2–4
Not specified
Weeks 2 onward: The line is pink or purple and can feel firm or lumpy.
Time to results
3–4 weeks to start
Lab report in 1–2 weeks
How long results last
Months; vitiligo color can be lasting
One-time test
Weeks into the course
Treated skin dries out and tans.
Not specified
After a missed session
Gaps matter.
Not specified
Risks
Risks
- A sunburn reaction
- Cold sores appearing
- Itching that is getting worse
- New or changing moles
- Eye irritation or vision change
- Polymorphic light eruption
- When to contact your provider
- Bleeding that will not stop
- Signs of infection
- The wound opening
- A stitch reaction
- A scar that is growing
- Numbness or tingling
Cost
Per session
Written estimate: Ask whether the quoted fee includes assessment, anesthesia, supplies, pathology when relevant, follow-up, and any planned repeat treatments.
In the US a punch biopsy usually produces two bills: the office fee, and a separate laboratory fee for reading the sample.
Insurance
This is one of the few treatments here that insurance often pays for, because it treats a medical condition.
Insurance normally covers it when there is a medical reason, subject to your deductible and copay.
Questions
Phototherapy
Punch Biopsy
Individual Questions
Is narrowband UVB the same as a tanning bed?
No. Tanning beds emit mostly ultraviolet A with a little UVB; this uses a narrow band around 311 nanometers chosen to keep the benefit and cut the burning wavelengths. Phototherapy doses are prescribed, recorded and adjusted, and areas that do not need treating are shielded. Tanning beds carry an established skin cancer risk.
How long before I see a difference?
Psoriasis usually starts improving by the third or fourth week and often clears over roughly 20 to 36 sessions. Eczema is slower, six to twelve weeks, with itch settling before the rash. Vitiligo cannot be judged before three months and often takes six to twelve months.
How often do I have to go?
Two or three times a week for most of a course. This is the hardest part, and the most common reason people stop, so be honest with yourself before starting and ask about a home unit if it will not work.
Does it cause skin cancer?
PUVA, the older tablet-plus-UVA treatment, clearly raises risk at high cumulative doses. Narrowband UVB studies have not shown a clear increase, but long-term data are limited, which is why lifetime sessions are counted, unaffected skin is shielded, and skin checks continue.
Can I do it at home?
Yes, with a prescription. Home units use the same lamps and dosing protocol, your dermatologist writes the schedule and reviews progress, and insurance sometimes pays because a unit costs less than a long series of office visits.
Will it come back after I stop?
Psoriasis and eczema usually return over weeks to months, and the length of the break varies a lot. Some people go onto a lower maintenance frequency instead of stopping. Pigment regained in vitiligo is often kept, though it can be lost if the condition is still active.
How big is a punch biopsy?
Usually 3 or 4 millimeters across — smaller than a pencil eraser. The skin is stretched first, so the round hole closes as a short straight line.
Does it hurt?
The numbing injection stings for a few seconds. After that you feel firm pressure and twisting, nothing sharp. Most people take nothing stronger than acetaminophen, on the first evening only.
Will I have stitches?
Usually one or two. On the face they come out at about 5 to 7 days, elsewhere at 10 to 14. Absorbable stitches dissolve on their own and are an option if getting back is hard.
Why did they biopsy a spot that looks fine instead of the worst patch?
For rashes, fresh untreated skin shows the diagnostic changes clearly, while the oldest patch has scratched, treated or healed skin over it. The site is chosen for what the pathologist needs to see.
What if the report does not name a disease?
Normal for rashes. The report describes a pattern that narrows the list, and the doctor combines it with what your skin looks like. Sometimes a second biopsy at a different stage settles it.
Will it leave a scar?
Yes — a small line or dot, a few millimeters. It stays pink for a couple of months, then fades. On deeper skin tones a brown mark is common for months, and raised scars are more likely on the chest, shoulders and upper back.
