The "rule of Ted" dictates that Ted cannot be harmed by his own ability.
Many evolved humans demonstrate immunity to various effects of their own special abilities, or the capability of using one's own ability without being harmed. Not all abilities come with such protection, however. Furthermore, immunity to the effects of one's own ability does not necessarily imply immunity to the effects of the same ability used by someone else.
Examples of Immunity
Mary Krause had acid running through her veins, and it never hurt her.
Linda Tavara could see the auras of others, but she never saw her own aura.
Tina Ramierez is able to exhale chlorine gas as opposed to carbon dioxide. Even though the haze is frequently drifting from right in front of her mouth and nose, she appears unaffected by it, whereas her victims are knocked out. (Viewpoints)
Peter Petrelli appears immune to some of his acquired abilities, but is not immune to others. He has demonstrated he cannot be affected by telepathic commands (Powerless), but lacks immunity to prevent others from hearing his thoughts (Fallout). Peter is also immune to time stops if he is within a certain distance of the individual who stops time (Powerless), but he can be brought as a passenger if someone else teleports (One of Us, One of Them). He is able to see others who are invisible if he is within a certain proximity (Godsend). Peter can, however, be affected by electric manipulation, telekinesis, and mental manipulation.
Peter is also immune to his own ability, he's not exposed to abilities acquired by future versions of himself, only to his original ability.
When Niki Sanders -- or her alternate personality Jessica -- performs feats of superhuman strength, she does not injure herself, even though the force she applies would sometimes be sufficient to break her own bones. Similarly, Knox is able to punch through steel without hurting his own hand.
El Diablo, and all others with this ability, can ignite their own bodies without getting burned.
Nathan is able to fly at apparently supersonic speeds without suffering any harm from friction with the atmosphere. Similarly, West is able to fly to altitudes of tens of thousands of feet without suffocating or freezing in the thin, cold atmosphere.
Tracy can freeze people, even to the point of killing them (The Butterfly Effect), but when she activates her ability, no part of her body even lowers in temperature (I Am Become Death). Contradictorily, when she freezes an entire parking garage, her body freezes as well (Cold Snap). However, Tracy also later reforms unscratched after being shot by Danko, shattering into pieces and melting back into a single entity. It should also be noted that her body was soaked with water at the time of her "cold snap".
Stephen Canfield is normally immune to the effects of his own vortices: when producing gravitational vacuums, he is generally not attracted towards them. He could, however, voluntarily cancel this immunity: he allowed one of his vortices consume him. (Angels and Monsters)
Ted was never harmed by his own ability: while his wife was poisoned by his radiation (Seven Minutes to Midnight), he remained healthy. He is also immune to the powerful explosions and extreme levels of heat caused by his ability. Ted was the epicenter of explosions in the Bennets' home (Company Man), FBI Headquarters (Seven Minutes to Midnight), and in front of his cabin (How Do You Stop an Exploding Man?, Part 2). Though these explosion burned and killed many people nearby, Ted walked away virtually unharmed.
Peter and Sylar have also absorbed and used this ability. Like Ted, neither of them ever had any negative effects from radiation they produced. Peter even exploded above New York City (How to Stop an Exploding Man), but suffered no discernible harm (Four Months Ago...), although he also had rapid cell regeneration at the time.
When Peter replicated this ability, it didn't nullify his ability as well. Also, he was able to replicate it in the first place despite his power supposedly being blocked, but René may have been purposely not blocking him.
Both Flint and Meredith appear unharmed by the fire and heat created by this ability. In fact, Meredith is even immune to the indirect effects of her ability, allowing her to breathe in a shipping container whose oxygen was consumed by her fire (One of Us, One of Them).
When Hiro or Peter stop time, everybody and everything around them freezes. However, when one of them stops time in the other's presence, both continue to move normally and can interact with each other. This usually happens involuntarily, (Collision), although in Once Upon a Time in Texas, Present Hiro froze time in the Burnt Toast Diner yet his past self also seemed to freeze with time.
When Daphne runs at superhuman speed, neither she nor anything she wears or carries takes any damage from air friction. She can also breathe normally while moving at superhuman speed and does not appear to tire even after running distances that would exhaust an ordinary human.
In addition, when Ando supercharged Daphne's ability, making her return several seconds in the past, they explained this through a theory in which Einstein states that if matter runs faster than the speed of light, it can travel through time. Normally, it would be impossible, because matter shatters at such high speeds. Daphne and Ando were perfectly unharmed with the time travel they did to 1991 (Dual).
Matt tries to send thoughts into Peter's mind, but is unsuccessful when Peter starts using the same ability to prevent it (Powerless). The ability to read the minds of people with the same ability can have different effects, and seems to be dependent on the level of control of those involved. In Fight or Flight, Matt tries to read Maury's mind, and they each experience a feedback, neither able to hear the other's thoughts. In The Second Coming, Matt tries to read Future Peter's mind, and is not only unable to, but experiences a feedback, whereas Future Peter seems to be completely unaffected. Also, while Matt and Peter both experienced feedback in trying to read Angela's mind when Arthur had her trapped in it, Matt was able to enter her mind with no feedback to battle Arthur and free her. In The Art of Deception, Peter replicates telepathy from Matt again and is able to immediatly read Matt's mind. He experiences no feedback from Matt's power and Matt doesn't even realize he's reading his mind until Peter tells him afterwards.
Examples of Lack of Immunity
Rollo Fusor's accomplice can be affected by her own ability. While she was able to normally touch herself, once she activated her power, Haram turned her hands towards her, dehydrating her until she died (Golden Handshake, Part 4). However, it has been noted that portions of the file that the Golden Handshake series is based on were falsified.
Elle could create electrical currents; usually Elle was not affected by her lightning, but she had the potential to be harmed nonetheless. Most notably, this happened when she is in contact with impure water, which made her unable to produce electricity without receiving part of her own electrical discharge (Cautionary Tales). Additionally, Elle was able to render Peter unconscious with her ability, despite him having absorbed it (Four Months Ago...). Elle was also able to feel the effects of her ability when she began to lose control of it (Sum Quod Sum, Part 1).
Although users of this ability are normally immune to its effects (Tracy Strauss's hands aren't even cold after she freezes a glass of water), if the user is wet during use of the ability, the user will also freeze due to the water. Later on, when she begins to lose control of her ability, Tracy's hands begin to freeze over even when they are not wet. Her entire body turns blue and she begins to show symptoms of hypothermia such as heavy breathing. (Brother's Keeper)
Eric Doyle specifically asks Michael whether he is immune to the lasers he generates. When he learns that Michael is not immune, Doyle proceeds to control his movements, murdering Michael by forcing him to shoot a laser at himself. (Doyle)
The Haitian was able to suppress Arthur's abilities, even though Arthur had that same ability. However, it should be noted that he soon found the feat difficult (Our Father). Peter was also exposed to the ability; nevertheless, the Haitian was still able to erase his memories and suppress his abilities.
While an agent's ability allows him to absorb all sound waves directed at him, including even Echo's devastating sonic blasts, he is not immune to the adverse effects of is power, rendering him permanently deaf. (Going Postal)
When Hiro froze time in the Burnt Toast Diner after he went back in time to save Charlie, he had to unfreeze his past self despite the fact that his past self possessed Space-time manipulation. (Once Upon a Time in Texas)
Matt and Peter were once capable of reading each other's thoughts although it causes pain and feedback (Fallout). Additionally, Maury is able to trap his son in a nightmare using his ability, even though Matt has the same ability, though Matt eventually uses this ability to escape (Fight or Flight). Matt later uses their mutual ability to escape another nightmare, leaving his father trapped in the dream. (Out of Time) Also, when Matt and Peter tried to read Angela's mind while she was trapped in it, both experience painful feedback although Peter did manage to see an image of the Pinehearst symbol. Also, when Peter replicated telepathy for the second time, he was able to read Matt Parkman's mind without any feedback or Matt even realizing it until he told him despite Matt possesing the same power. However, in this case Matt may not have blocked him as he simply didn't realize what Peter was doing. (The Art of Deception)
"So, tell me, are you one of these guys immune to your own power?"
"Oh my God."
"Hmmm... Guess not."
- While Ted, Peter, and Sylar are immune to their ability to generate radiation, Amid Halebi from the unaired pilot had severe radiation burns on his hands.
- Writers Aron Coleite and Joe Pokaski commented in an interview about the ability immunity demonstrated by some evolved humans, calling it the "rule of Ted", in reference to Ted Sprague's ability to be unharmed by the radiation he creates. The writers said "the oven can't be hurt by the heat".
- Immunity to the harmful side effects of flight may even apply to passengers, as Matt seems completely unaffected by flying with Nathan, despite traveling from New York to Texas in a short time. (Powerless)
- Immunity to the harmful side effects of super speed may even apply to passengers, as Flint doesn't seem to be affected by moving at high speeds with Daphne. (Dying of the Light)
- The level of immunity to telepathy seems to depend on the levels of control of those using it. In Fallout, Matt was still trying to understand and control his ability, and Peter wasn't even aware he had it. The result was a feedback for them both, and each hearing the other's thoughts. In Fight or Flight, when a more experienced Matt tries to read Maury's mind, they each experience a feedback, neither able to hear the other's thoughts. Maury had a very high level of control over his power. In The Second Coming, Matt's level of control has progressed greatly, but Future Peter has had four more years to perfect the power. This results in Matt not only failing to read Future Peter's thoughts, but experiencing a painful feedback, while Future Peter seems to be completely unaffected. When Peter read Matt's mind to find Sylar in The Art of Deception, he did so without any side-effects, but given Matt's reaction, he wasn't expecting Peter to do that and didn't block him.
- Although Elle felt the effects of her power as she uncontrollably electrocuted herself, her skin did not burn as Claire's did when the ability was used on her. (Eris Quod Sum)