T20.4
Corrosion of unspecified degree of head, face, and neck
T20.4 is a non-billable ICD-10-CM code header for corrosion of unspecified degree of head, face, and neck. Report a more specific code from it instead. It is part of the FY2027 code set, effective October 1, 2026. The more specific codes under it are T20.40 Corrosion of unspecified degree of head, face, and neck, unspecified site; T20.41 Corrosion of unspecified degree of ear [any part, except ear drum]; T20.42 Corrosion of unspecified degree of lip(s); T20.43 Corrosion of unspecified degree of chin and 5 more. Its coding notes include a Code first instruction, a Use additional code instruction and 5 Excludes2 entries.
7th characters
Every code below needs one of these (defined at T20).
The appropriate 7th character is to be added to each code from category T20
- Ainitial encounter
- Dsubsequent encounter
- Ssequela
Guidelines tips
From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.
The 7th character depends on whether the patient is in active treatment, not on who sees the patient. An aftercare Z code is not used for injury aftercare.
Burns are classified by depth, extent and agent. Burns of the same site and side but different degrees take the highest degree. Non-healing burns are coded as acute burns.
Late effects of burns are coded with 7th character S, and a current burn and a sequela of an old burn can be coded together. An external cause code is used with burns.
Code first
If the underlying condition listed here is present and known, sequence it first.
- (T51-T65) to identify chemical and intent
Use additional code
Add the listed code as a secondary code, if known.
- external cause code to identify place (Y92)
Also from chapter/block level (2 notes)
- code to identify any retained foreign body, if applicable (Z18.-)
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
Also from chapter/block level (2 notes)
- birth trauma (P10-P15)
- obstetric trauma (O70-O71)
Includes
Further defines or gives examples of the content of the category.
Also from chapter/block level (3 notes)
- burns and corrosions of first degree [erythema]
- burns and corrosions of second degree [blisters][epidermal loss]
- burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss]
Notes
Also from chapter/block level (2 notes)
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
More specific codes under T20.4 9
- T20.40Corrosion of unspecified degree of head, face, and neck, unspecified site7th char needed
- T20.41Corrosion of unspecified degree of ear [any part, except ear drum]Header
- T20.42Corrosion of unspecified degree of lip(s)7th char needed
- T20.43Corrosion of unspecified degree of chin7th char needed
- T20.44Corrosion of unspecified degree of nose (septum)7th char needed
- T20.45Corrosion of unspecified degree of scalp [any part]7th char needed
- T20.46Corrosion of unspecified degree of forehead and cheek7th char needed
- T20.47Corrosion of unspecified degree of neck7th char needed
- T20.49Corrosion of unspecified degree of multiple sites of head, face, and neck7th char needed