"Unwell," Not "Sick": OET Clinical Register

“The patient has been feeling sick for the past week.” Nothing in that sentence is ungrammatical. It is also not how one clinician describes another patient’s condition to a colleague, and in British English it may not even mean what the writer intended. This is the unwell vs sick distinction in OET writing: a small, specific word swap that sits at the centre of Genre & Style, one of the six official criteria examiners mark OET Writing scripts against.

Watch the full breakdown: “Unwell,” Not “Sick”: OET Clinical Register works through the distinction with real OET-style letter sentences.

Why does “sick” read as the wrong register in OET writing?

Genre & Style is the criterion that checks whether your letter sounds like genuine clinical correspondence — one healthcare professional writing to another — rather than a diary entry, a text message to a friend, or a GP describing their own symptoms out loud. It sits alongside Purpose, Content, Conciseness & Clarity, Organisation & Layout, and Language as one of the six official criteria an OET Writing script is marked against.

“Sick” fails this test quietly, because it is not an obviously informal word the way slang is. It is a perfectly ordinary, perfectly correct word — which is exactly why it slips past a normal proofreading pass. The problem is not that “sick” is wrong English. The problem is that it is the register a patient uses to describe themselves (“I’ve been feeling sick all week”), not the register a nurse, doctor, or physiotherapist uses to describe that same patient in a referral or discharge letter. “Unwell” is the clinical equivalent: the same idea, pitched at the register the reader — another healthcare professional — expects.

This sits next to the broader over-formality and under-formality issues covered in our professional tone guide, and it follows the same shape as the specific-phrase problem in our “kindly note” register guide: a word or phrase that is grammatically blameless but belongs to the wrong genre for a clinical letter.

Unwell vs sick in OET writing: what’s the real difference?

Both words describe a patient who is not well. They are not, however, interchangeable in register or, in British English, always even in meaning. The table below sets out the distinction examiners are trained to notice.

The pattern across the table is consistent: “unwell” is the default clinical word for general illness, and “sick” survives only where English has no other option — fixed administrative compounds, the specific meaning of nausea, or a direct quotation of what the patient actually said.

Why does “feeling sick” cause a specific ambiguity in British clinical English?

This is the part of the rule that goes beyond register and into meaning. In British English, “feeling sick” is not a general synonym for “feeling unwell” the way it sometimes functions in casual speech elsewhere. It specifically means nauseous — close to vomiting. A British-trained reader, including an OET examiner marking against British and Australian English conventions, will read “the patient has been feeling sick for three days” as a report that the patient has been nauseous for three days, not that the patient has generally been unwell for three days.

This creates a real risk beyond Genre & Style: if you mean “generally unwell” but write “sick,” you may be making an unintended clinical claim. A referral letter that says “the patient has felt sick since Monday” when the actual presenting complaint is fatigue and low-grade fever has introduced a symptom — nausea — that may not belong in the letter at all. This overlaps with the Content criterion, because an inaccurate symptom description is a content problem, not only a style one. “Unwell” avoids the ambiguity entirely: it means “not well,” full stop, with no narrower reading attached.

When is “sick” actually correct in an OET letter?

“Sick” is not banned from OET writing. It has a real, correct role in three situations, and candidates who over-correct by deleting every instance of “sick” sometimes introduce a different error by avoiding a word that was actually needed.

1. Administrative compounds. “Sick leave,” “sick note,” “sick pay,” and “sick list” are fixed terms with no clinical-register substitute. Write “The patient was issued a sick note for two weeks,” not “an unwell note.”
2. Reporting nausea specifically. If the patient’s actual complaint is nausea, “sick” or “sickness” is the accurate word, not “unwell.” “The patient has felt sick and vomited twice since this morning” correctly reports a nausea symptom.
3. Direct quotation. If you are quoting the patient’s exact words, keep them in quotation marks even if they use “sick” where you would otherwise write “unwell”: “The patient described herself as “sick as a dog” since the weekend” preserves the patient’s voice inside reported speech, which is a legitimate and sometimes useful technique in a case-note summary.

Outside those three situations — anywhere you are describing the patient’s overall condition in your own narrative voice — “unwell” is the word examiners expect.

How does this connect to the Genre & Style criterion?

Genre & Style sits alongside Purpose, Content, Conciseness & Clarity, Organisation & Layout, and Language as one of the six official OET writing criteria, and our Genre & Style score guide covers how the 0–7 band is assigned in full. Word-pair errors like unwell vs sick are a recurring feature of that criterion because they are, individually, small. A single use of “sick” instead of “unwell” will not sink a script on its own. The problem is that register habits repeat: a candidate who writes “sick” once in a draft letter typically writes it three or four times, alongside other everyday-register choices — “tummy” for “abdomen,” “tired” for “fatigued,” “getting worse” for “deteriorating.” Examiners are trained to read for the pattern across a whole letter, not just a single sentence, and a cluster of casual-register word choices reads as a genre problem even when every individual sentence is grammatically correct.

This is also why the error is hard to self-correct. “The patient felt sick” sounds completely natural to the person who wrote it, because it is natural, correct, everyday English. The mismatch only becomes visible when you read the sentence the way the intended reader — a receiving clinician — would read it, which is a different skill from checking grammar or spelling.

A quick self-check for “sick” in your draft

Because “sick” is grammatically invisible to a spellchecker or grammar tool, check for it manually with a short, targeted pass before you submit:

1. Search your letter for every instance of “sick.” Note each one before deciding anything.
2. Ask what each instance actually means. If it means “generally unwell,” replace it with “unwell.” If it specifically means “nauseous” or “vomiting,” leave it as “sick” — that’s the correct word for that meaning.
3. Check for fixed compounds. “Sick leave,” “sick note,” “sick pay,” and “sickness” (as in morning sickness or motion sickness) are correct as written — don’t force “unwell” into a compound where it doesn’t fit.
4. Check for direct quotes. If “sick” appears inside quotation marks reporting the patient’s own words, it’s correct and should stay exactly as the patient said it.

This takes under a minute once you know what to search for, and it catches a register error that a standard grammar check has no way of flagging, because nothing about “the patient felt sick” is grammatically wrong. For the broader set of everyday-to-clinical vocabulary swaps beyond this one pair, our OET writing vocabulary guide covers the Language-criterion word list candidates most often need, and our Genre and Style mistakes guide looks at the wider set of register errors beyond single word pairs.

The honest limit of self-editing for register

Register errors like unwell vs sick are difficult to catch on your own precisely because the sentence never sounds wrong to the person who wrote it. “I’ve been feeling sick” and “the patient felt sick” are both completely natural things to say — the issue only appears when you read the sentence as the intended reader, a receiving clinician, would read it.

The free Writing Checker is a useful first pass for surface issues like spelling and basic grammar, but register judgement calls like unwell vs sick are exactly what a full criterion-by-criterion review is built to catch. Our OET writing correction service reviews your actual letter against all six official criteria, including the everyday-register word choices that sound fine to the writer and read as a Genre & Style flag to the examiner.