Why when we have a fever we say

I have a fever.

But when I have diarrhea we say

I have diarrhea.

Why don't we say

I have a diarrhea.

Is there any rule? If I come across a new symptom, how do I decide whether to add "a" or not adding it into my sentence?

  • Why are the names of the disease all in small letters?
    – Ook
    Mar 18, 2016 at 5:24
  • 1
    They aren't proper names. But for example Parkinson's disease would because it was named for someone.
    – user3169
    Mar 18, 2016 at 20:46
  • 1
    See more discussion of a closely related question at ell.stackexchange.com/questions/82976/…
    – Adam
    Mar 22, 2016 at 7:02

2 Answers 2


I have diarrhea.

is correct. Disease names do not use an article (for example cancer, diabetes, hepatitis, pneumonia, etc).

I have a fever.

Descriptive conditions do (for example headache, broken arm, strained back, etc.)

  • The patient complained of early fatigue, cardiac discomfort and palpitation. (descriptive conditions? )
    – V.V.
    Mar 19, 2016 at 3:53
  • Perhaps the patient had the mumps. Or the measles. Or the Spanish flu. (In most case the dichotomy presented in this answer is correct, but there are exceptions.)
    – Adam
    Mar 22, 2016 at 7:06
  • The exceptions you spotted almost always swing both ways. "I had mumps" et alis, is also correct. ("I have a cancer" is a bit archaic, but also valid.) (See V.V.'s answer) "A lesion" vs. "lesions" seems to be the general rule with exceptions for things like named diseases.
    – The Nate
    Apr 5, 2017 at 20:15

Yes, there's a rule.With a plural (countable) noun you should use an article. The first noun is countable in this meaning (if you aren't sure,consult a good dictionary).The second noun is a mass noun.You don't need an article here.

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