How to make this persistent damage?

What I am asking, is if every two seconds you're standing on this, it takes away 10 health.

2 Seconds = 10 damage

function onTouched(hit)
	local humanoid = hit.Parent:findFirstChild("Humanoid")
	if (humanoid ~= nil) then
		humanoid.Health = humanoid.Health - 10
	end
end

script.Parent.Touched:connect(onTouched)

if (humanoid ~= nil) then while true do humanoid.Health = humanoid.Health - 2 wait(2) end

If you want to stop at a certain point then do the for i = 1,5