Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Elsewhere, contact your local poison centre or emergency medical service.
Call emergency services now if there is:
These symptoms do not always require an ambulance unless breathing is affected or the person is severely unwell.
And for anyone, someone who:
Treat any possible swallowing of drain cleaner as urgent.
In the United States, call Poison Control at 1-800-222-1222 .
Do not wait for symptoms.
Eye exposure needs immediate rinsing and urgent expert advice, especially if pain, blurred vision or redness continues.
Significant skin burns, blistering or ongoing pain also require urgent assessment.
After initial treatment, contact the treating service promptly for increasing pain, fever, vomiting, weight loss, food sticking or new difficulty swallowing.
Follow-up may include checking nutrition, swallowing and healing after an internal burn.
Keep appointments even if symptoms improve.
Every sign above is quoted from the sofidex article on Drain cleaner poisoning. If you are not sure, err upward — it is always reasonable to be checked.