Ultraviolet light reaches the immune cells sitting in the skin and slows them down. In psoriasis and eczema it reduces the number of active T cells — the white blood cells driving the inflammation — and cuts the chemical signals that make skin red, thick and itchy. The light only travels a millimetre or two, so the effect stays in the skin. It is not a drug circulating through your body, which is why it can be used in people who cannot take immune-suppressing tablets, including many people who are pregnant.
"Narrowband" means the machine puts out only wavelengths right around 311 nanometres. Older phototherapy used a much wider slice of ultraviolet light, most of which caused burning without adding benefit. Narrowing the band gives the useful effect at a much lower total ultraviolet dose. Vitiligo works differently: the same light nudges surviving pigment cells that live deep in the hair follicles to multiply and spread out across the pale patch. That is why repigmentation shows up first as small dots scattered inside a patch rather than the whole patch filling in evenly.
Bring every medicine and supplement you take to the first appointment. Light-sensitising drugs are common and easy to miss, and they change the starting dose.
Expect a starting dose set from your skin tone, or from a small test patch. Deeper skin tones start at a higher dose and can usually go up faster, because more pigment means more natural protection.
Tell the clinic if you burn easily, have had skin cancer, or have a strong family history of melanoma.
Do not put anything on your skin beforehand unless your clinic tells you to. Thick creams and ointments block or scatter the light and change the dose you actually get. Some clinics ask for a thin layer of plain mineral oil on scaly plaques — follow their instruction, not a general rule.
Skip sunscreen on the areas being treated. Use it on your face if your face is not part of the problem.
No tanning beds and no deliberate sunbathing during your course. That extra ultraviolet is not counted in your dose, and it is how burns happen.
Wear or bring what you need to shield the parts that are not being treated. Genital skin is shielded for men as standard. Ask for a face shield if your face is clear.
You undress to the areas being treated and step into the cabinet, or sit in front of the panel. Most units are a standing booth lined with vertical bulbs.
You put on the goggles the clinic gives you. This is not optional — ultraviolet light damages the surface of the eye, and the goggles are the reason eye problems are rare.
The staff shield anything that does not need treating. Genitals are covered for men at every session. If your face is clear, ask for it to be shielded too, since facial skin picks up plenty of ultraviolet over a lifetime already.
The machine runs for a set time. The first sessions are often under 30 seconds. As your dose is increased, sessions grow to a few minutes at most. You stand still and turn if asked.
It does not hurt. Most people feel mild warmth. If you feel stinging or burning during the session, say so — that is a sign the dose is too high for you and it should be adjusted.
You dress and leave. Including undressing and dressing, most appointments take ten to fifteen minutes. The realistic time cost is the travel, not the treatment.
There is no recovery period. You can drive, work and exercise straight afterwards.
Some pinkness for a few hours after a session is normal and expected — it is a sign the dose is close to right. It should fade by the next day.
Skin usually gets drier over a course. Moisturise daily, just not in the hour before a session.
You will tan. Narrowband UVB darkens the skin, and this is unavoidable. It also means the dose is adjusted as you go, because tanned skin absorbs less.
If a session leaves you sore, tender or pink into the next day, tell the clinic before the next visit. They will hold the dose steady or step it back rather than continuing to increase it.
Psoriasis and eczema: itch usually eases first, often within two to three weeks. Visible clearing of plaques and patches builds between weeks four and eight. Most people reach their best result somewhere between 20 and 30 sessions. If nothing has moved after about 20 sessions at a proper dose, it probably is not going to.
Vitiligo: this is slower and needs patience. The first sign is small freckle-like dots of colour appearing inside a pale patch, usually after two to three months. Face and trunk respond best. Hands, feet and lips often respond poorly no matter how long you continue. Six months of treatment is a reasonable point to judge whether it is worth continuing.
How long results last is the honest catch. This is a treatment that controls disease while you are having it. Psoriasis commonly returns within three to six months of stopping, though some people get a much longer break. Eczema behaves similarly. Repigmented vitiligo holds up better than the others, but some patches can fade again.
Many people move onto a maintenance schedule — one session a week or every two weeks — instead of stopping outright. Others do a course each winter and go without in the summer.
Home narrowband UVB units are real medical devices, not a workaround. They are prescribed regularly, they use the same bulbs as clinic machines, and for a condition needing months of treatment they often work out cheaper and get used more consistently than a clinic course. A handheld wand suits a few patches; full cabinets exist for widespread disease. They come with a dosing schedule from your dermatologist, and they need the same goggles, the same shielding and the same slow dose increases. Used casually, they burn people.
A tanning bed is not a substitute, and this is the most important sentence on this page. Tanning beds put out mostly UVA with a small amount of unfiltered UVB, which is close to the opposite of what narrowband UVB is designed to do. There is no dosing, no shielding, no one watching your skin, and the cancer risk is well established rather than debated. Some people with psoriasis do notice a temporary improvement from a tanning bed, and that is exactly why the idea sticks around — but you are paying for that improvement with a much higher ultraviolet dose than any dermatologist would give you.
Red light and LED devices sold for skin do not treat any of these conditions. They are a different part of the light spectrum entirely and do nothing for psoriasis, eczema or vitiligo. Sunlight itself does help some people with psoriasis, and dermatologists sometimes suggest short, careful sun exposure — but that is a rough substitute, not a measured one.