The B00-B09 ICD-10 codes cover viral infections that show up on the skin and mucous membranes, the block that runs from herpes simplex through to unspecified viral rashes. If you code dermatology, pediatrics, primary care, or urgent care, you meet this range constantly: chickenpox, shingles, measles, warts, cold sores, and hand, foot and mouth disease all live here. This guide breaks the block down category by category, shows which codes bill on their own and which need more digits, and flags the Excludes1 traps that cause denials.
Answer the two questions every one of these codes asks: which virus is it, and how specific is the documentation? Get those right and the rest falls into place.
Key takeaways
- The block B00-B09 classifies viral infections characterized by skin and mucous membrane lesions.
- Categories run B00 (herpes simplex), B01 (varicella), B02 (zoster), B03 (smallpox), B04 (mpox), B05 (measles), B06 (rubella), B07 (viral warts), B08 (other specified), and B09 (unspecified).
- Some are three-character billable codes; others need a fourth or fifth character before you can submit them.
- Excludes1 notes push several conditions elsewhere, such as anogenital herpes to A60 and congenital herpes to P35.2.
- Reach for B09 only when the documentation genuinely will not support anything more specific.
What do the B00-B09 ICD-10 codes cover?
First, some orientation. This block sits in Chapter 1, the chapter for infectious and parasitic diseases (A00 to B99). Every code in it describes a viral illness whose hallmark is a rash, blister, sore, or lesion on the skin or a mucous membrane. That shared feature, in short, is why smallpox and molluscum contagiosum sit in the same neighborhood as measles.
Before you assign anything, it helps to know how the code is put together. Each category starts with the letter B and two digits, and many add a decimal point plus one or two more characters for the specific type, site, or complication. Our walkthrough on how ICD-10 codes are structured covers that anatomy if you want a refresher.
The block at a glance
| Category | Condition | Billing note |
|---|---|---|
| B00 | Herpesviral [herpes simplex] infections | Needs a 4th character (for example B00.9) |
| B01 | Varicella [chickenpox] | Needs a 4th character (B01.9 without complication) |
| B02 | Zoster [herpes zoster], or shingles | Needs a 4th or 5th character |
| B03 | Smallpox (eradicated, retained for history) | Three-character billable code |
| B04 | Monkeypox (mpox) | Three-character billable code |
| B05 | Measles | Needs a 4th character (B05.9 without complication) |
| B06 | Rubella [German measles] | Needs a 4th character |
| B07 | Viral warts | Needs a 4th character (B07.0 plantar wart) |
| B08 | Other specified viral skin and mucous membrane infections | Needs a 4th character (B08.1, B08.4, B08.5) |
| B09 | Unspecified viral infection with skin and mucous membrane lesions | Three-character billable code |
Which B00-B09 codes bill on their own?
Among the B00-B09 ICD-10 codes, a three-character category is billable only when it has no further subdivisions. In this block, for example, B03, B04, and B09 are complete at three characters. Every other category, however, is a header: you cannot submit a bare B00 or B02, because the code set expects you to add the specificity that lives in the fourth and fifth characters.
That distinction matters on the claim. A clearinghouse rejects a truncated code before it ever reaches the payer, so always carry the category down to its most specific valid code. When you are unsure whether a code is complete, verify it against the current 2026 ICD-10-CM code list.
The codes you will assign most often
Realistically, a handful of the B00-B09 ICD-10 codes account for most of your daily volume. So it pays to know these categories cold before the busy season hits.
B00: herpes simplex
B00 captures cold sores, herpetic gingivostomatitis, herpetic whitlow, and eczema herpeticum, among others. B00.9 covers an unspecified herpesviral infection. Watch the Excludes1 note: anogenital herpes belongs to A60, and congenital herpesviral infection goes to P35.2. Neither one gets a B00 code.
B01 and B02: chickenpox and shingles
B01 is varicella (chickenpox), with B01.9 for a case without complication and other subcodes for complications like varicella pneumonia or encephalitis. B02 is zoster (shingles) from the same virus reactivating years later. B02 subdivides for complications, including postherpetic neuralgia and ocular disease, so read the note for nerve or eye involvement before defaulting to B02.9. The CDC shingles resource is a useful reference when the documentation is thin on complications.
B05 and B06: measles and rubella
B05 is measles and B06 is rubella. Both subdivide by complication, so B05.9 or B06.9 apply only when the record shows no complication. Given renewed measles activity, precise coding here feeds public health reporting, not just the claim.
B07: viral warts
B07 covers common viral warts, with B07.0 for plantar warts, B07.8 for other viral warts, and B07.9 for an unspecified wart. Anogenital (venereal) warts are excluded and route to A63.0 instead.
B08: the catch-all with familiar diagnoses
B08 gathers specified viral infections that do not have their own category. Three of its subcodes come up constantly: B08.1 for molluscum contagiosum, B08.4 for hand, foot and mouth disease, and B08.5 for herpangina (enteroviral vesicular pharyngitis). Pediatric and urgent care coders lean on these year-round.
B09: the last resort
B09 reports an unspecified viral infection with skin and mucous membrane lesions. It is billable, but treat it as a fallback. If the provider named the virus or the classic presentation, a more specific code almost always exists. For the deeper cut on the herpes and pox side of this block, our companion guide to the B00 to B07 viral infection codes goes further into the subcategories.
Excludes1 traps that trigger denials
In particular, the block leans on Excludes1 notes, which mean “not coded here, ever.” The ones that bite most often:
- Anogenital herpesviral infection goes to A60, not B00.
- Congenital herpesviral infection goes to P35.2.
- Anogenital (venereal) warts go to A63.0, not B07.
Miss one of these and you either overcode or land the diagnosis in the wrong chapter, which can stall a claim or misrepresent the encounter. When two codes seem to fit, the Excludes1 note is the tiebreaker.
How to pick the right B00-B09 code, step by step
In practice, the B00-B09 ICD-10 codes reward a simple, repeatable routine. Therefore, run every viral skin case through the same five steps before you finalize the claim.
- Identify the virus or the named condition from the provider’s documentation.
- Match it to the correct category, B00 through B09.
- Check for an Excludes1 note that sends it elsewhere.
- Add the fourth or fifth character for the specific type, site, or complication.
- Confirm the final code is complete and billable before you submit.
Frequently asked questions
What does the B00-B09 range represent in ICD-10-CM?
The B00-B09 ICD-10 codes represent viral infections characterized by skin and mucous membrane lesions. Specifically, the block includes herpes simplex, varicella, zoster, smallpox, mpox, measles, rubella, viral warts, and related conditions.
Is B09 a billable code?
Yes. B09 is a valid three-character billable code for an unspecified viral infection with skin and mucous membrane lesions, but you should use a more specific code whenever the documentation supports one.
What ICD-10 code is hand, foot and mouth disease?
Hand, foot and mouth disease is B08.4, which sits in the B08 subcategory for other specified viral skin and mucous membrane infections.
Why can’t I bill a plain B00 or B02?
Those categories are headers that require more specificity. You must add the fourth or fifth character (for example B00.9 or B02.9) before the code is complete and billable.
Where do anogenital herpes and genital warts go?
Anogenital herpesviral infection is coded to A60, and anogenital (venereal) warts are coded to A63.0. Excludes1 notes route them out of the B00-B09 block.
Putting the block to work
The B00-B09 ICD-10 codes look busy at first, but the logic is steady: name the virus, respect the Excludes1 notes, and carry every category to its most specific billable code. In addition, keep B09 in your back pocket for the rare case with no detail, and lean on the specific subcodes for the everyday diagnoses like shingles, warts, and hand, foot and mouth disease. As a result, this block becomes one of the easier corners of Chapter 1 to code cleanly.
