IGA grade
The five-point scale dermatology research uses to grade acne in clinical trials. Knowing where you sit on it tells you more than any count ever will.
Definition
IGA stands for Investigator Global Assessment. It is a five-point ordinal scale dermatology research uses to grade the severity of acne in a single assessment moment. It goes from 0 (clear) to 4 (severe). The FDA recognizes IGA as a primary endpoint in acne clinical trials, which is why most published acne research reports IGA changes alongside lesion counts.
The five grades
| Grade | Severity | What it usually looks like |
|---|---|---|
| 0 | Clear | No inflammatory or non-inflammatory lesions, may have a few residual marks |
| 1 | Almost clear | Rare non-inflammatory with no more than one small inflammatory lesion |
| 2 | Mild | Some non-inflammatory lesions, no more than a few inflammatory lesions, none of which are nodulocystic |
| 3 | Moderate | Up to many non-inflammatory and many inflammatory lesions, no more than a few nodulocystic lesions |
| 4 | Severe | Many non-inflammatory and many inflammatory lesions including multiple nodulocystic lesions |
Why IGA is useful
A lesion count tells you 'there are 24 papules and 6 pustules today.' That is a measurement of breadth but not of the lived experience. IGA grade compresses lesion count, depth, distribution, and inflammation into a single global judgment. Two people can have similar lesion counts but very different IGA grades because one has deep nodulocystic lesions and the other does not. Treatment guidelines often key off the IGA grade rather than the lesion count.
How clinical trials use IGA
The primary endpoint of most published acne trials is the proportion of patients who reach IGA 0 or 1 (clear or almost clear) at twelve weeks, often combined with a two-grade improvement from baseline. When a study reports 'X percent of patients improved by two IGA grades,' that is the metric being talked about. It is the same scale used for retinoids, antibiotics, isotretinoin trials, and combination therapies.
How Trace uses IGA
Trace assigns an IGA grade on every daily scan along with the per-category lesion counts. The grade and the counts can move differently. The grade dropping from 3 to 2 over thirty days while you tested a single new product is the kind of result a clinical trial would report. You see it on a phone, on yourself, with your data.
Trace produces an IGA estimate from a standardized selfie, not a clinical exam. A dermatologist examining you in person remains the gold standard for grading decisions that matter. This is glossary content, not medical advice.
Frequently asked
What is the difference between IGA grade and lesion count?
Lesion count is a number (how many comedones, papules, pustules, nodulocystic). IGA grade is a single five-point judgment of how severe the overall picture is, including depth and distribution that pure counting misses. Clinical research usually reports both.
Why is IGA used in clinical trials?
It compresses a lot of clinical information into a single ordinal grade, which makes comparing treatment groups straightforward. The FDA recognizes it as a primary endpoint for acne studies.
Does Trace produce an IGA grade?
Yes. Trace estimates an IGA grade on every daily scan, on device, alongside the count of each lesion type. The trend across thirty days is the unit of meaningful change.