Saitama has never been shown to be sick or even affected by sickness.
Saitama has shown symptoms of low mood, a loss of pleasure in activities, slowed speech and paralysis. All these symptoms are indicative of depression. Despite his depression, Saitama hasn't let it stop him from being a hero and striving to make the world a better place.
Saitama vs cat
[ Still trying to do the math on how, the only thing to ever actually damage Saitama in the series is a cat scratching his face.
Saitama, for all intents and purposes, is still human in terms of his physiology and biological needs. That means that he still needs to breathe air to survive. Nevertheless, he was able to survive on the Moon without breathing because he was holding his breath the entire time.
He is immortal, so he must live forever... His power isn't all about his body, but he is rather healthy, considering he's still doing his workout, so i reckon somewhere above 100 years, considering he's as normal as everyone else when it comes to basic human things.
Saitama has never been shown to be sick or even affected by sickness.
Under the Hero Association, he is assigned the hero name Caped Baldy (ハゲマント, Hagemanto; Viz: Bald Cape) and is currently A-Class Rank 39.
Saitama, being someone who is capable of shaping the entire world, feels pain when he lands awkwardly. Similarly, he also expressed his pain when a cat scratched his face.
Now, readers learned that not only Saitama is capable of suffering, but he is also afraid of completely losing his humanity, and this is why he kept close to friends like Genos, King, and even Bang, despite his apparent annoyance towards them.
Since then, he hasn't lost any of those fights in the series. However, the only fight that came close to testing his true potential was his fight against Garou in the Monsters Association arc of One Punch Man.
In the opening sequence of the first episode of the One-Punch Man anime, viewers are introduced to Saitama as a downtrodden, unemployed youth in search of a job. His depression is so severe that he doesn't feel any emotion when confronted by an evil crab monster.
After saving the life of a young kid, he decided to become a hero. In that endeavor, Saitama wanted to improve his endurance and strength. He persisted with a mind-boggling routine of 100 pushups, 100 sit ups, 100 squats and 10 kilometers of running. Apparently, this workout regime is the reason why he went bald.
Saitama is also concerned with the kind of hero he wants to be. It turns out, having unconquerable strength has done nothing but blindside him to not only real world problems but the problems within himself: he struggles with depression and anxiety.
Not only did he survive, he also managed to defeat Cosmic Fear Garou and blow up Jupiter in the process. Saitama obliterated a planet by sneezing, and this is yet another indication that he was able to breathe in outer space.
However, Garou proves too powerful for Blast, and he uses Gravity Fission Nuclear Fission attack to dominate the S-class hero. Garou now realizes that Saitama wasn't fighting at his full potential. So, to bring out the baldy's real strength, Garou kills Genos by taking out his core.
Boros was the first enemy who survived a normal punch from Saitama, a notable feat considering all of the previous disasters had been obliterated, while Boros simply had his armor destroyed by the first punch. In fact, Boros was hit with 3 Normal Punches, 1 Consecutive Normal Punches, and 1 Serious Punch.
This comes from Saitama's rigorous, albeit simple, work-out regimen. Indeed, he's withstood the best that his opponents have given him, and rarely comes away with a scratch. Accordingly, there is no evidence suggesting that he would be physically unable to withstand even his own attack in One-Punch Man.
Saitama, also known by his hero name Caped Baldy, and also as One Punch Man, is the titular protagonist of the webcomic/manga/anime series One Punch-Man, and the most powerful known being in the series.
Saitama may or may not be able to feel pain, and there is no confirmation on this because he has never once displayed any discomfort regardless of who he's fighting. The man has no idea what tiredness means, as seen when he runs vast distances without sweating or losing his breath.
Yes. Basically because he's invincible/immortal. It's similar to Popeye when he eats Spinach . With it he wouldn't die in any way.