Nickel is a transition metal widely distributed in the environment, air, water, and soil, and can originate from natural sources or human activities. While nickel is ubiquitous, its role as a trace element for humans and animals is not yet recognized. Nickel exposure can lead to various health effects, including allergies, cardiovascular and kidney diseases, lung fibrosis, and cancer. The mechanisms of nickel toxicity are not fully understood, but mitochondrial dysfunction and oxidative stress are considered key factors. Recent studies suggest that nickel exposure can induce epigenetic changes that disrupt the genome. This review aims to describe the chemical properties of nickel in humans and its toxicity mechanisms, as well as strategies for removing nickel from the environment, such as phytoremediation and phytomining. Nickel exists in various oxidation states, with Ni²+ being the most common in the environment. It is found in nature in combination with oxygen and sulfur, and is used in various industrial applications. Nickel is essential for plant growth and has vital roles in various physiological functions, but high levels can be toxic. Nickel is used in a wide range of applications, including jewelry, stainless steel, and batteries. Nickel is also a component of many environmental sources, such as stainless steel kitchen utensils, tobacco smoke, and dietary exposure through food. Nickel toxicity and carcinogenicity are well-documented, with high incidence of nasal and lung cancer in workers exposed to nickel. Nickel nanoparticles are associated with reproductive toxicity and can cause lung toxicity, inflammation, oxidative stress, and apoptosis. The International Agency for Research on Cancer (IARC) classifies nickel compounds as carcinogens. Nickel can enter the body through inhalation, ingestion, or dermal absorption, with inhalation being the most dangerous route. Nickel allergy is common, with women being more prone to it than men. Nickel is a common allergen in jewelry, coins, and orthodontic materials. Nickel allergy can cause contact dermatitis, hypersensitivity, and DNA damage. Prevention strategies include reducing exposure to nickel-containing items and using formulations that prevent nickel penetration through the skin. Nickel has epigenetic effects, including DNA methylation, histone modification, and microRNA expression, which can influence gene expression and contribute to cancer. Nickel compounds can induce histone hyperphosphorylation, hypermethylation, and hyperubiquitination, leading to epigenetic changes that may cause cell transformation and tumor progression. Nickel compounds are teratogenic, causing congenital malformations and stillbirths in embryos. Exposure to nickel during pregnancy can lead to malformations in the fetus, including hydrocephaly, microphthalmia, and exophthalmia. Nickel-induced apoptosis is a key mechanism of toxicity, with nickel ions causing mitochondrial damage and activating caspases that lead to cell death. Nickel phytoremediation and phytomining are strategies for removing nickel from the environment. Phytoremediation uses plants toNickel is a transition metal widely distributed in the environment, air, water, and soil, and can originate from natural sources or human activities. While nickel is ubiquitous, its role as a trace element for humans and animals is not yet recognized. Nickel exposure can lead to various health effects, including allergies, cardiovascular and kidney diseases, lung fibrosis, and cancer. The mechanisms of nickel toxicity are not fully understood, but mitochondrial dysfunction and oxidative stress are considered key factors. Recent studies suggest that nickel exposure can induce epigenetic changes that disrupt the genome. This review aims to describe the chemical properties of nickel in humans and its toxicity mechanisms, as well as strategies for removing nickel from the environment, such as phytoremediation and phytomining. Nickel exists in various oxidation states, with Ni²+ being the most common in the environment. It is found in nature in combination with oxygen and sulfur, and is used in various industrial applications. Nickel is essential for plant growth and has vital roles in various physiological functions, but high levels can be toxic. Nickel is used in a wide range of applications, including jewelry, stainless steel, and batteries. Nickel is also a component of many environmental sources, such as stainless steel kitchen utensils, tobacco smoke, and dietary exposure through food. Nickel toxicity and carcinogenicity are well-documented, with high incidence of nasal and lung cancer in workers exposed to nickel. Nickel nanoparticles are associated with reproductive toxicity and can cause lung toxicity, inflammation, oxidative stress, and apoptosis. The International Agency for Research on Cancer (IARC) classifies nickel compounds as carcinogens. Nickel can enter the body through inhalation, ingestion, or dermal absorption, with inhalation being the most dangerous route. Nickel allergy is common, with women being more prone to it than men. Nickel is a common allergen in jewelry, coins, and orthodontic materials. Nickel allergy can cause contact dermatitis, hypersensitivity, and DNA damage. Prevention strategies include reducing exposure to nickel-containing items and using formulations that prevent nickel penetration through the skin. Nickel has epigenetic effects, including DNA methylation, histone modification, and microRNA expression, which can influence gene expression and contribute to cancer. Nickel compounds can induce histone hyperphosphorylation, hypermethylation, and hyperubiquitination, leading to epigenetic changes that may cause cell transformation and tumor progression. Nickel compounds are teratogenic, causing congenital malformations and stillbirths in embryos. Exposure to nickel during pregnancy can lead to malformations in the fetus, including hydrocephaly, microphthalmia, and exophthalmia. Nickel-induced apoptosis is a key mechanism of toxicity, with nickel ions causing mitochondrial damage and activating caspases that lead to cell death. Nickel phytoremediation and phytomining are strategies for removing nickel from the environment. Phytoremediation uses plants to