Practice: bpùat, jèp and mêuay
What you will be able to do
Choose between ปวด, เจ็บ and เมื่อย from the symptom itself, keep ปวดคอ and เจ็บคอ apart, and build the เป็น conditions without breaking ท้องเสีย.
Thai has three words for hurt and they are not degrees of the same thing. ปวด is deep and dull with no edge, เจ็บ is sharp and on the surface, เมื่อย is muscle tiredness from use. The verb goes straight in front of the body part, and how bad it is is a separate word.
Which verb?
A headache that throbs on its own while nothing is touching it
ปวด (bpùat) is the deep one: under the surface, no edge you could draw round, beating on its own. ปวดหัว (bpùat hǔa) is not three words waiting for a fourth, it is a finished sentence meaning I have a headache. เวียนหัว (wian-hǔa) is the other thing a head does and it is not a pain at all — it is the room going round, so it sends a doctor looking somewhere else entirely.
Which verb?
You have cut your finger on a tin lid
Anything with a wound, a burn or a bite is เจ็บ (jèp) whatever else it feels like, because the surface is broken and that settles it. เจ็บ is the sharp one, the word for anything with a surface.
Which verb?
Your legs after four hours on a bike, and a firm thumb pressed into them would feel good
เมื่อย (mêuay) is the muscle one: what a body part feels like after it has been used, tiredness in the meat of the thing rather than damage to it. เมื่อยขา (mêuay khǎa), my legs ache from walking. The test that separates it from the other two is what a firm thumb would do: pressing a เจ็บ is unbearable, pressing a เมื่อย is the reason massage shops exist.
Which one?
The ache that comes from inside the tooth and keeps you awake
ฟัน takes all three of these and they are three different complaints. ปวดฟัน (bpùat fan) is toothache, the deep kind from inside the tooth. เจ็บฟัน (jèp fan) is what you report when they press it or when biting on that side hurts, because that pain arrives from outside. เสียวฟัน (sǐao fan) is the short electric zing off something cold, which is neither an ache nor a sharp hurt.
Which one?
A sore throat
เจ็บคอ (jèp khaw) is a sore throat. คอ is the neck and the throat, one word for both, so the verb in front is the only thing that tells a pharmacist which shelf to walk to. ปวดคอ (bpùat khaw) sends her to the stiff-neck shelf, and เมื่อยคอ (mêuay khaw) is the third thing คอ can do: the tired, worked neck you get off a screen or a bad pillow, which is muscle and not throat.
Which one?
A neck that aches deep and on its own — not the tired neck a massage would fix
ปวดคอ (bpùat khaw) is a stiff neck, เจ็บคอ (jèp khaw) a sore throat. Same body word, two complaints that have nothing to do with each other, and only the verb tells them apart. This is the pair worth drilling until it is automatic. เมื่อยคอ (mêuay khaw) is the third thing คอ does, and the thumb test separates it — pressing a เมื่อย is the reason massage shops exist.
Which one?
A stomach ache, somewhere between the ribs and the hips
ปวดท้อง (bpùat tháwng) is the ordinary way to report it, and the word does not tell a doctor which organ, so expect them to find it by pressing. ตึง (dteung) is tight rather than painful, the feeling in ตึงๆแต่ไม่เจ็บ. The belly is the one place the two hurt verbs overlap: เจ็บท้อง (jèp tháwng) is ordinary too and nobody will correct you. คลื่นไส้ (khlêun-sâi) is nausea, a different complaint altogether — it has no place to put a finger on, so it cannot answer ตรงไหน (dtrong nǎi).
It does hurt. What do you answer?
กดตรงนี้เจ็บไหมครับ
Echo the verb they used. Thai has no all-purpose yes, so the answer is เจ็บครับ or ไม่เจ็บครับ. They said เจ็บ rather than ปวด because they are touching you.
What do you say?
You have a fingertip on the exact spot, and pressing it makes it worse
เจ็บตรงนี้ (jèp dtrong-níi), it hurts right here, said with the finger already on the spot: one fingertip covers it and pressing makes it worse, which is the whole test. ปวดตรงนี้ is the deeper kind, and the lesson's own contrast line is ปวดตรงนี้ครับ กดแล้วไม่เจ็บ, it aches here but pressing does not hurt. ตรงไหน (dtrong nǎi) is the question coming back at you, not your answer, and pointing while you speak is not a failure of Thai.
Which sentence?
It aches deep inside, with no edge, and it hurts a great deal
The three verbs are not a scale. เจ็บ is not worse than ปวด: they name the character of the sensation, and how bad it is is said separately, after the verb, with มาก (mâak) or นิดหน่อย (nít-nàwy). So the deep edgeless ache picks the verb and a great deal picks the intensity word, and ปวดนิดหน่อย would be the right kind of hurt with the wrong amount.
Is this how it is said?
ปวดที่หัวครับ
Put nothing between the verb and the body part. Thai puts the hurt verb first and the body part straight after it, with no preposition, no my and no subject, then the particle: ปวดหัวครับ. Adding ผม (phǒm) at the front does not repair it either, because ที่ is still sitting where nothing should sit, and the subject only makes the sentence heavier.
Which one?
a fever
Conditions rather than sensations take เป็น (bpen): เป็นไข้ a fever, เป็นหวัด a cold, เป็นผื่น a rash, เป็นแผล a wound. มีไข้ (mii khâi) is equally normal and equally yours to say; it says the temperature is up rather than naming the illness.
Which one do people actually say?
Diarrhoea, two days now
ท้องเสีย (tháwng-sǐa) is the exception in the เป็น set. It is already a verb phrase, ท้อง plus เสีย, so it stands on its own and takes the มา … แล้ว duration frame directly, and เป็นท้องเสีย is not what people say. ตั้งแต่ (dtâng-dtàe) is the other frame and it wants a starting point rather than a stretch: ตั้งแต่เมื่อคืน since last night, ตั้งแต่เช้า since this morning.
You have no allergies. What do you do?
แพ้ยาอะไรไหมคะ
Say the words: ไม่แพ้ครับ (mâi pháe khráp) if you are not, and the name if you are. แพ้ is a plain verb, so it takes plain ไม่; ไม่ใช่ (mâi châi) is the one that rejects a noun and it does not fit here. A nod or a shake is not an answer, and this is the one question where a misread reply is dangerous. The question comes back before every prescription and every injection.
Common mistake
Do not treat the three as a scale. เจ็บ is not worse than ปวด: they name the kind of sensation, and severity is said separately with นิดหน่อย (nít-nàwy) or มาก (mâak). Put nothing between the verb and the body part, so ปวดหัว and never ปวดที่หัว. Do not build เป็นท้องเสีย, because ท้องเสีย already contains its own verb. And the belly is the one place ปวด and เจ็บ genuinely overlap, where ปวดท้อง and เจ็บท้อง are both ordinary, so do not go looking for a rule there. The pair that does not blur is ปวดคอ, a stiff neck, against เจ็บคอ, a sore throat.