Damage over time

Damage over time (often refered to as DoT) is a damage inflicted continuously over a period of time. Unlike the other three damage sources, damage over time does not hit.

Mechanics
All damage over time effects are a kind of debuff. A creature can have multiple applications of these debuffs of the same type but usually only the one with the highest damage per second works at any given time (except for poison where all applications stack cumulatively); this is true even in the case of effects applied by different players or sources.

For example, if two players each apply the ignite status ailment to the same target, only the higher damage per second of the two ignites will affect the target, at least until the higher fades and leaves the second ignite to become the new highest. In this context, two damage over time effects are to be considered the same only if they have the same name; a target may be affected by multiple effects that deal burning damage (such as, ignite and burning ground).

On kill effects
In case of an enemy being killed by damage over time while being affected by multiple DoT effects, the kill is attributed to the owner of the effect that was inflicted first.

Damage over time kills from non-character sources like minions and totems will give the kill and any on kill effects to the owner of the totem or minion. This is a limitation of the game and not an intended game mechanic.

Damage scaling
The following modifiers will directly affect the damage over time; note that some of these modifiers apply only to the DoTs whereas some may also apply to the skill that triggered it:
 * (e.g. or )
 * (e.g. or )
 * if applied by a trap
 * if applied by a mine
 * if applied by a totem
 * if applied by a minion
 * if applied by a totem
 * if applied by a minion

Natively modifiers to attack damage (i.e. weapon damage, melee damage, etc.) and spell damage do not apply to damage over time effects unless specifically stated so, as observed on skills like, or.

Damage conversion does not apply to damage over time. Flat damage from things like does not apply to damage over time.

Modifiers that increase damage over time will not affect the damage a character deals to himself with skills like or, as that particular effect is considered a part of the buff and not a part of player's damage output. However, modifiers that increase/reduce damage taken will affect it.

Duration
Tampering with the duration of a damage over time effect will affect the total amount of damage dealt by it but not its damage per second. The exception to this is the modifier (as seen on  and ), which will 'speed up' ignites inflicted by the player, increasing their damage per second at the cost of duration, leaving the total amount of damage unchanged.

Conditional modifiers
There are modifiers that can apply their effects only when a certain condition is met. Modifiers that are conditional on properties of the target do not affect damage over time because only hits are able to check someone else properties.

Some examples:
 * from
 * from

Graphic Clarification
Visual clarification by Mark (a developer at GGG) for the changes coming with 3.0.

https://www.pathofexile.com/forum/view-thread/1897612/page/4#p14474050

Math

 * Modifiers that say increased damage over time multiplier are not additive with modifiers that do no include the word "multiplier".

Interactions

 * "% Chance to deal double damage" will not affect damage over time, because it does not hit.
 * Most damage over time snapshots.

Other skills

 * can cast an aura that deals damage over time as well.

In addition, many skills are capable of applying damage over time effects through ignite, poison and bleed: Attacks made with weapons crafted with an will inflict decay, dealing chaos damage over time.
 * ignite - requires fire damage (e.x. through damage conversion or ) as well as chance to ignite (e.x. ) or a critical strike
 * poison - requires physical damage and/or chaos damage as well as chance to poison (e.x. )
 * bleed - requires physical damage and a chance to bleed (e.x. )

Base items
The following base items are related to damage over time:

Cluster jewel passives
The following cluster jewel-only passives are related to damage over time:

Version history

 * Generic modifiers to damage dealt will now apply to damage over time that your character causes. Damage over time is not spell damage, nor attack damage, so modifiers specific to those types will not apply. Non-specific "increased damage" modifiers will apply to damage over time. Type-specific modifiers will apply as well. For example, "increased fire damage" modifiers will apply to fire damage over time.
 * }