What happens if I use Lay on Hands to cure one disease when there are in fact multiple?

Question

A new player of mine asked me this question:

If I use Lay on Hands to cure what I assume is one disease, but it's actually at least two with similar symptoms, which disease gets cured?

• Do I target one symptom and the disease that carried that symptom gets cured (which may or may not be the whole set of diseases)?
• Is it selected randomly?

Do I learn in the process that there are two separate diseases and have the chance to expend 5 more points during the same action?

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For this particular situation assume that the detect poison and disease spell may not be available for whatever reason. Some situations include

• Not prepared
• Antimagic area
• No spell slots to spare and no time to set up a ritual

Answer 1

Character Knowledge guides you

In order for the Paladin to use their Lay on Hands to remove (or attempt to remove) a poison/disease, the Paladin needs to believe that there is a disease, poison, or multiple of them to remove.

The only way they'd know this (in character) is if the targeted creature has told them, or if they perceived an event/symptom that would suggest the creature has a poison or disease effect.

Now that we've established the prerequisite of knowledge, it becomes easy to determine which poison or disease is cured because the paladin will have stated what they are curing.

Knowing the Unknown (DM adjudication)

If the Paladin or the affected creature thinks they may have a disease or poison, then set a DC and let them do a medicine to see if they discover it. The tricky part here is that a failed roll doesn't mean there isn't a disease, just that they don't know if there is. And they won't know if a roll has failed or if they know there is no problem.

But if they neither have any reason to check, and do not check, then there is no way for the Paladin to know there is something in need of a cure.

Gotta have faith

If the paladin isn't sure, they can just drop the resource cost and 'cure' the target. Again, they won't know if the target is cured or if they didn't have anything at all. You just gotta have faith that the Paladin healed you :)

Answer 2

Symptoms are your friend, and the DM is responsible for narrating how this occurs.

Diseases and poisons which have debilitating effects on a character will normally have noticeable symptoms. In fact, the symptoms will usually be so noticeable that there won't be a check required to verify that the character is suffering from something even if you don't know specifically what it is.

Remember, rolls are for when the outcome is in doubt. If a character is feeling ill, that's not in doubt. That's something you have told them due to the nature of their disease/poison. For example: If my character is shaking uncontrollably, but otherwise feels "fine", I'm going to ask my paladin to try fixing me. No roll required, I suspect I'm suffering from something thanks to losing control of my limbs.

This is where the Paladin's lay on hands can come into play. Paladin uses lay on hands to remove a poison/disease, and sees some symptoms abate. For example: the patient is suffering from a high fever, has large pupils in a brightly lit room, is shaking uncontrollably, and their lips have turned purple. After the Paladin uses lay on hands, the lips return to their normal colour and the shaking abates, but the fever and pupils remain. This is now an indicator of a secondary effect persisting on the patient.

None of this would require rolls as the outcome isn't uncertain. They're simply observations made due to obvious symptoms.

In your case, if the two diseases/poisons exhibit similar symptoms, your Paladin shouldn't notice a change after using lay on hands. If the Paladin uses it a second time, that's when they should notice the change. As for whether or not the Paladin is aware that they've successfully removed a disease/poison with lay on hands, the text here:

You can cure multiple diseases and neutralize multiple poisons with a single use of Lay on Hands, expending hit points separately for each one.

... implies rather heavily that the Paladin is fully aware of how many diseases/poisons are currently affecting the target at the time of the feature use. Thematically I would be described it as follows:

"You lay your hands on Auriga, attempting to cleanse whatever is infesting her body bringing about her illness. A surge of power (5 HP) courses from you and cleanses some of the poison you feel coursing through her system. You consider her physical appearance and note she still looks ill. A second surge pulses into her (another 5HP from the same application of lay on hands) and you feel the darkness grasping at her vitality slither away in defeat. Her face takes on a relaxed look of comfort and she seems to be faring well, the disease/poison having been cleansed from her system."

Mechanically your player would be asking things like:

P: I use lay on hands, is she cured?

DM: No. The symptoms persist after the first 5HP.

P: I spend another 5 to cleanse any additional effect. Is she cured?

DM: Yes, the symptoms have abated.

P: Ok, I apply 10 HP to my usage of Lay on Hands.

DM: Narrates using the above.

Remember, in 5e the process is as follows:

DM describes the situation. Player describes what they want to do. DM narrates the results. In this situation, the character being healed had persistent symptoms after the first application of lay on hands, so the player would simply keep applying it to keep removing diseases/poisons until they either succeeded, or ran out of healing power to do so. It's up to the DM to narrate how it happens thematically.

Answer 3

The rules don't specify, but there are other resources available

The Cleric, Druid, Paladin, and Ranger all have access to a first level spell Detect Poison and Disease¹. Assuming that it isn't available overlooks how Druids, Clerics, and Paladins get their spells. (With the Ranger, the problem is more acute). In some cases, getting that prepared on the next rest will be helpful; in other cases it won't.

They can't wait! Have the player(s) make a Wisdom(Medicine) check

Call for a medicine check(roll), or apply a passive medicine check as the DM.

Medicine.
A Wisdom (Medicine) check lets you try to stabilize a dying companion or diagnose an illness.

This is one of those ability checks where the "help" function (roll with advantage, or +5 to a passive score) and the application of the guidance cantrip (add 1d4 to the roll for the check) may help the paladin, or other healer, diagnose the afflicted character. In particular, if the paladin has cured one disease, noting that the creature/character is still sick is a good use of the passive Medicine check by you, the DM. (You indicated that you are asking as DM). (Passive checks; basic rules p. 59, Working Together, p. 59)

If the Paladin/party does not make use of the spell before healing via lay on hands, and/or misses on the medicine check, a disease is still cured but the rules don't specify which one: the DM will need to make a ruling regarding which one gets healed. (That's how it's handled: make a ruling).

It would be reasonable to rule that, if the Paladin specifies a particular disease by knowing what it was (saw a sewer rat bit a character, so specifies healing sewer plague) that is the cured disease. If an aboleth's tentacle inflicted a disease, and the paladin knows this by seeing the slime, the paladin specifying that cure is fair. Likewise with an Otyugh's bite.

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¹ Detect Poison and Disease

For the duration, you can sense the presence and location of poisons, poisonous creatures, and diseases within 30 feet of you. You also identify the kind of poison, poisonous creature, or disease in each case.

If the party applies the spell (it has the ritual tag, so it can be done without burning a slot if there is a ritual caster) then the other disease(s) can be discovered if the infection/agent for that disease was previously unknown.