Penetration Ref /26
Resistance Penetration
Penetration causes the target's corresponding Resistance to be treated as lower than its actual value by the specified amount when of calculating Damage taken from your Hits. Resistances can only be Penetrated down to a minimum of 0% by default.

Since Penetration only affects Hits and applies to the target's defensive stats rather than your own offensive stats, it does not affect damage with Ailments.
(60–100)% increased Energy Shield
+(60–100) to maximum Mana
(10–15)% increased Rarity of Items found
Your Hits can Penetrate Elemental Resistances down to a minimum of -50%
Supports any skill that Hits enemies, making those Hits Penetrate enemy Fire resistance.
Supports any skill that Hits enemies, making those Hits Penetrate enemy Cold resistance.
Supports any skill that Hits enemies, making those Hits Penetrate enemy Lightning resistance.
15% increased Duration of Ailments against Enemies with Exposure
20% increased chance to inflict Ailments against Enemies with Exposure
Ignite
Ignite is an Ailment that deals Fire damage over time, and lasts for 4 seconds by default.

The chance for a Hit to Ignite a target is determined by the total Magnitude of Flammability on the target, including the amount added by that Hit.

Fire damage from Hits Contributes to the Magnitude of Ignite, so Hits dealing more Fire damage inflict stronger Ignites.
The base Magnitude of Ignite is Fire damage per second equal to 20% of the Fire damage dealt by the Hit that inflicted it. This is calculated using the final damage dealt by the Hit, but not any modifiers on the target that affect how much damage they will take from the Hit. This Magnitude is not further affected by any modifiers to the damage you deal.

Modifiers and Debuffs that affect the enemy's ability to mitigate damage (such as Shock) can affect the damage the enemy takes from Ignite, but any such modifiers that specifically apply to Hit damage (such as Penetration) do not affect Ignite damage.
Poison
Poison is an Ailment that deals Chaos damage over time, and lasts 2 seconds by default. Damage from Poison bypasses Energy Shield.

Physical and Chaos damage from Hits Contribute to Poison Magnitude.

Damage does not Contribute to Poison chance, so it cannot be inflicted without an explicit source of Poison chance.

The base Magnitude of Poison is Chaos damage per second equal to 20% of the Pre-mitigation Physical and Chaos damage of the Hit that inflicted it. This magnitude is not further affected by any modifiers to the damage you deal.

Modifiers and Debuffs that affect the enemy's ability to mitigate damage (such as Shock) can affect the damage the enemy takes from Poison, but any such modifiers that specifically apply to Hit damage (such as Penetration) do not affect Poison damage.
Resisted by Other Value
Damage from your Hits will effectively ignore the value of the target's relevant Resistance, and instead be mitigated by the specified value of Resistance.

This will still occur even if you Ignore the target's Resistance, as this mitigation is not based on their Resistance stats. Similarly, Penetration will not apply to this Resistance value.
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