Vitiligo is typically diagnosed through a visual skin examination by a dermatologist, often without the need for lab work or a biopsy. The condition produces distinctive milky-white patches with sharp, well-defined edges that are usually recognizable on sight. In most cases, a dermatologist can confirm vitiligo in a single office visit using a combination of your medical history, a physical exam, and a specialized ultraviolet lamp.
What the Skin Examination Looks Like
The first step is a thorough look at your skin under normal lighting. A dermatologist will check for the hallmark sign: smooth, completely white patches that have lost all pigment. These patches most commonly appear on the hands, feet, arms, and face, but they can show up anywhere on the body, including inside the mouth or on the scalp. The texture of the skin itself stays normal. There’s no scaling, no raised edges, no itching.
Your doctor will also note the pattern. In the most common form, patches appear symmetrically on both sides of the body. If you lose pigment on one knuckle of your left hand, you’ll often see it on the same knuckle of the right hand. A less common form, called segmental vitiligo, affects only one side or one area of the body, like a single leg or one side of the face. These two patterns behave differently over time, so distinguishing them matters for predicting how the condition will progress.
Some variants have additional visual cues. Trichrome vitiligo, for example, shows three distinct shades: normal skin, a tan or light brown transitional zone, and fully white skin. This pattern tends to appear on the trunk and signals that the vitiligo is actively spreading.
How a Wood’s Lamp Helps
After the initial visual exam, your dermatologist will likely use a Wood’s lamp, a handheld device that emits long-wave ultraviolet light. The room is darkened, and the lamp is held a few inches from your skin. Under this light, vitiligo patches glow a striking bright blue-white with sharply defined borders. This fluorescence comes from the complete absence of melanin in those areas.
The Wood’s lamp is especially useful in two situations. First, it reveals patches that are too faint to see under normal room lighting, particularly on people with fair skin. Early or subtle patches that might otherwise go unnoticed become obvious under UV light. Second, it helps distinguish vitiligo from other conditions that cause lighter skin. A birthmark called nevus depigmentosus, for instance, only glows a dull off-white because it still contains some pigment. The white spots associated with tuberous sclerosis also look different under the lamp. This contrast between a bright blue-white glow and a muted off-white glow gives the dermatologist confidence in the diagnosis.
If you use sunless tanning products to cover vitiligo patches, the lamp can see through the cosmetic layer. The tanning chemical fluoresces salmon-colored while vitiligo patches remain blue-white underneath, allowing your doctor to assess the true size of affected areas.
Ruling Out Other Conditions
Several other skin conditions cause white or light patches, and part of diagnosing vitiligo is making sure it isn’t something else. The most common look-alikes include tinea versicolor (a fungal infection) and post-inflammatory hypopigmentation (lighter patches left behind after eczema, burns, or other skin injuries).
- Tinea versicolor produces small, scaly patches that may be lighter or darker than surrounding skin. The edges blend unevenly rather than forming a crisp border, and the patches often itch, especially in hot or humid weather. Because it’s caused by a fungus, a simple skin scraping can confirm it under a microscope.
- Post-inflammatory hypopigmentation leaves lighter (but not completely white) patches in areas where the skin was previously inflamed or injured. The color difference is subtler than vitiligo, and there’s usually a clear history of a rash or wound in that spot.
- Pityriasis alba causes pale, slightly scaly patches most often seen on children’s faces. The patches are not stark white and tend to resolve on their own.
Vitiligo stands apart from all of these because the patches are completely depigmented (not just lighter), smooth (no scaling or flaking), and painless (no itch). If there’s any diagnostic uncertainty, a small skin biopsy can settle the question. Under a microscope, vitiligo skin shows a total absence of functioning melanocytes, the cells that produce pigment. Newer or actively spreading patches may also show immune cells clustered along the border where pigmented skin meets depigmented skin, a sign that the immune system is actively destroying melanocytes.
Blood Tests for Related Conditions
Once vitiligo is confirmed, your dermatologist will likely order blood work. This isn’t to diagnose vitiligo itself, but to screen for other autoimmune conditions that tend to occur alongside it. Thyroid disease is the most significant concern.
In studies of vitiligo patients, about 15% tested positive for antibodies against thyroid peroxidase, a marker for autoimmune thyroid disease. Your doctor will typically check thyroid-stimulating hormone (TSH) and may test for those thyroid antibodies as well. Other tests sometimes included are blood sugar levels (about 8% of vitiligo patients in one study had elevated levels), vitamin B12, and folic acid, though low levels of these don’t appear to drive vitiligo itself. Antinuclear antibodies (ANA), which screen broadly for autoimmune activity, were positive in roughly 18% of vitiligo patients in the same study.
These blood tests don’t change the vitiligo diagnosis, but they can catch a thyroid problem or other condition early, before symptoms develop.
Tracking How Much Skin Is Affected
After diagnosis, your dermatologist may formally measure the extent of your vitiligo using a scoring system called the Vitiligo Area Scoring Index, or VASI. This provides a baseline number that helps track whether the condition is stable, improving with treatment, or spreading.
The system divides the body into five regions: hands, upper extremities, trunk, lower extremities, and feet. Your doctor estimates the percentage of each region affected, using the palm of your hand (which represents roughly 1% of total body surface area) as a measuring guide. Within each patch, the degree of pigment loss is graded on a scale from specks of depigmentation (10%) to complete white-out (100%). The combined score ranges from 0 to 100. This scoring is most useful when you’re starting treatment, because repeating it months later shows whether repigmentation is actually happening.
Signs of Active or Spreading Vitiligo
Part of the diagnostic picture is determining whether your vitiligo is currently active or stable, since this influences treatment decisions. Several clues point to active disease. The Koebner phenomenon, where new white patches develop at sites of skin injury, is one of the most telling. If you notice depigmentation forming along a scratch, cut, sunburn, or area of chronic friction (like a waistband or bra strap), that suggests your immune system is actively targeting melanocytes wherever the skin is stressed.
Other signs of progression include patches with a trichrome appearance (that three-zone color gradient mentioned earlier), patches with slightly inflamed or pink borders, and rapid expansion of existing patches. Your dermatologist may note these features during the exam or ask you to photograph your patches monthly so changes over time become easier to track. Segmental vitiligo, by contrast, typically spreads within its limited area for a year or two and then stabilizes permanently.