Maslow's hierarchy of needs is a theory in psychology that suggests that humans have five levels of needs, the most basic being physiological. First are the physiological needs, which are classified as food, water, breathable air, warmth/coolth, sexual expression, and sleep. The next level up consists of safety needs which consist of protection from dangerous elements such as weather or predators. Belongingness and love need are social needs that include friends and family or just an individual's desire for affection or companionship. The fourth level is self-esteem which includes accomplishment and mastery over one's environment/life. Finally at the top is self-actualization which includes realizing personal potential through creativity and problem-solving abilities.