Question Do we use 'motsu' or 'aru' in terms of intangible things like allergies and stomach aches?

[OnAndOnItGoes]

私はナッツアレルギーがあります
私はナッツアレルギーを持っています

It makes sense to me to use aru as one would use for inanimate objects but I wondered if because a person is the subject that changes?
Saying it exists rather than I possess one right? Any help thoroughly appreciated!

 

[Majestic]

Both are understood, and (I think) are both equally fine. Toritoribe-san may have to correct me on that.
Actually, you can even shorten it further and say 私はナッツアレルギーです.
I know it sounds as if you are saying you yourself ARE the allergy, but in Japanese the context is clear, and its understood that you are talking about an affliction you have.

 

[Toritoribe]

Yes, both expressions work well for アレルギー, and 私はナッツアレルギーです is very commonly used.

As for stomach aches, the nuance is different between ある and 持つ. While 胃痛がある/胃に痛みがある expresses the present state, 胃痛を持つ/持っている is often used for chronic symptoms. Especially, the noun form 胃痛持ち (私は胃痛持ちです) means they have stomach aches chronically, thus, it doesn't always mean they have a stomach ache now.

You can also use する. This is more common than ある especially for head aches (頭痛がする). The most common expression is body part が痛い (胃が痛い, 頭が痛い) for the present state, though.

 

[OnAndOnItGoes]

Yes, both expressions work well for アレルギー, and 私はナッツアレルギーです is very commonly used.

As for stomach aches, the nuance is different between ある and 持つ. While 胃痛がある/胃に痛みがある expresses the present state, 胃痛を持つ/持っている is often used for chronic symptoms. Especially, the noun form 胃痛持ち (私は胃痛持ちです) means they have stomach aches chronically, thus, it doesn't always mean they have a stomach ache now.

You can also use する. This is more common than ある especially for head aches (頭痛がする). The most common expression is body part が痛い (胃が痛い, 頭が痛い) for the present state, though.

Thank you very much this is incredibly helpful. My little brain was running in circles but that makes perfect sense. I love how context can take out pieces of information like that haha what a riot! I'm encouraged to press on in my studies.