One story says Goddess Durga has incarnated as little Kātyāyanī — daughter of sage Katyayan — to destroy all arrogant evil demonic forces of the world, in her real form as Durga, she killed many demons that were sent by Kaalkeya.

A demon named Jwarasur, the demon of fever, started spreading incurable diseases to Katyayani's childhood friends, such as cholera, dysentery, measles, and smallpox. Katyayani cured the diseases of some of her friends. To relieve the world from all fevers and diseases, Katyayani assumed the form of Shitala Devi. Each of her four hands held a short broom, winnowing fan, jar of cooling water and a drinking cup. With her power, she cured all the children's diseases. Katyayani then requests her friend, Batuk to go out and confront the demon Jwarasur. A battle ensued between the young Batuk and demon Jwarasur. Jwarasur succeeds in defeating Batuk. Then, Batuk, lying dead, magically faded into dust. Jwarasur was shocked that Batuk had disappeared and wondered where he had gone, not realising that Batuk had, in fact, assumed the form of an awful male figure with three eyes and four arms holding a battle-axe, sword, trident and demon head. This figure was pitch-black in colour with flowing locks and eyes ablaze with fury and wore a tiger-skin and a garland of skulls - for Batuk had assumed the appearance of Lord Shiva's ferocious form, the terrible Bhairav. Bhairav reprimands Jwarasur and tells him that he is the servant of Goddess Durga (incarnate as Katyayani). A long discussion ensued but then converted into battle. Jwarasur created many demons from his powers but Bhairav managed to destroy all of them. Finally, Bhairav wrestled with Jwarasur and killed him with his trident.

There once was a demon named Jwarasur. He was named Jwarasur because he is the demon of fever. He went around and spread incurable fever to all the children of their parents wherever he went. His terrifying presence alarmed those who were around him and none of the children ever got relieved because of him. Mothers were crying and they wailed, and doctors couldn't find a cure for the children's incurable fever. Knowing that Jwarasur's reign of terror will keep spreading, Mahadev and Parvati decided to take action against him to stop him. Parvati decides that the power of her coolness will bring relief to all the children and their parents. Mahadev transformed himself into Bhairav and reaches the battlefield where he confronted Jwarasur to prevent him from going around and doing any more harm to children. Both of them indulged themselves in a great and huge wrestling match.

Meanwhile, Parvati on the other hand, transformed herself into Sheetala Devi. Sheetala Devi resembles a maiden, she was fair in complexion, wearing light and dark blue robes, wearing a minimal amount of ornaments on her limbs, three-eyed and is looking very youthful in appearance while representing an omnipotent Goddess, as being one among the incarnations of Durga. In her four hands, she held a bowl, a fan, a small broom, or a winnowing fan of some sort and she carries a pot of cold water, in which she uses to cure the diseased. She was mounted on the back of a donkey as her vehicle. Goddess Sheetala started her mission on providing relief to the children. Wherever Goddess Sheetala went around and over the world, with her most effective tool, her cold and cooling water brought relief to all children, of all shapes, sizes, colors, and ages. They were all completely restored to their good health, which brought instant relief to them and to joy to all the parents. Seeing Goddess Sheetala, everybody paid their homage to her and all the children thanked her for curing their incurable fever and purifying them.

Then, Goddess Sheetala makes an appearance in the battlefield where Bhairav and Jwarasur were fighting against each other. Sheetala Devi berates Jwarasur for his misdeeds towards young children as he spread fever to them. Bhairav also lets Jwarasur know that not only can Goddess Sheetala cure poxes, sores, ghouls, pustules and diseases, she is a goddess of sores, ghouls, and diseases and she can give them too. She is the cause as well as the cure. Finally, Sheetala Devi severely infected Jwarasur with an intense case of smallpox, thus putting an end to his reign of terror for once and for all. Mahadev liberates himself from Bhairav and Parvati frees herself from Goddess Sheetala Devi. They both returned home to Kailash.