Hypodermic theory
The hypodermic needle theory is a model of communication that suggests that the recipient directly receives an intended message and fully accepts it. The theory is associated with the work of Harold Lasswell, who as a researcher and publicist strongly focused on the analysis of propaganda, in a period marked by world tensions between the wars and concern about the effects of journalistic mediations on the formation of public opinion.
Concept
This theory of direct influence effects was based on early observations of the media effect, as used by Nazi propaganda and Hollywood effects in the 1930s and 1940s. It was assumed that people were "uniformly controlled by their 'instincts' biologically based and that reacted more or less uniformly to any 'stimulus' to be presented". The theory graphically assumes that the media message is a bullet fired from the "media gun" towards the "head" of the viewer. Similarly, the same idea of the "shooting" paradigm is also used. It suggests that the media injects its messages directly into the passive audience. This passive audience is immediately affected by these messages. The public essentially cannot escape the influence of the media and is therefore considered a 'sitting duck'. This theory suggests that the public is vulnerable to messages thrown at them due to the limited communication tools and studies of the effects of the media on the masses at that time. It means that the media explores information in such a way that it is injected into the minds of the audiences like bullets.
Origins
The theory of the "hypodermic needle" was created to study how propaganda affected citizens in the 1920s. and 30'. This theory develops between the First and Second World Wars. The tragedies of these wars gave rise to the need to study the effects that propaganda generated at that time.
Goebbels was responsible for propagating and popularizing the ideas of the Nazi party, even before it came to power. In 1933 the Nazis came to power and Goebbels was appointed Minister of Public Instruction and Propaganda. In this way he became head of the press, radio, cinema, theater and virtually all cultural and scientific activities. He used practically all the means at his disposal to give credibility to the Nazi movement, he measured consequences, sifted information and theorized about the phenomenon of mass communication by defining its basic points: advantages and disadvantages of information, audience, opinion, channel, message., response, etc.
The hypodermic theory is a post hoc theory, since it was defined after World War I, after seeing the effects that propaganda had in this conflict. The First World War involved a great deployment of weapons, money, etc. and it was a great social loss. At that time, Britain and the US had not experienced war in a long time. Another peculiarity of this war is that it took place very close to the civilian population, so it became necessary to give importance to the war that it did not really have. To achieve this, propaganda was used in a society in which ties were increasingly difficult, to convince people to give their lives in a global conflict that, in the end, would only be beneficial to a few.
At the end of the war, in Great Britain, the United States and Germany, people began to reflect on this enormous bombardment of propaganda, as a means of manipulating people, by governments and the media, and Thus begins the criticism and formulation of the theory.
Main reference
Harold Lasswell (1902 - 1978). He is considered one of the founding fathers of communication research for his work on propaganda and political communication. He was one of the most influential activists of the need to develop research in communication and played an important role in launching the institutionalization of these studies. Precisely, in one of his studies on propaganda, published in 1927, he said: "...When all objections have been discarded, and when all extravagant estimates have been reduced to the essential, the fact remains that propaganda is one of the most powerful instruments of the modern world.
Characteristics of the hypodermic theory
The irrational processes explained by the neurobiological paradigm; the characteristics of a mass society, marked by isolation and alienation; and the spectacular development of the media make the hypodermic theory perfectly reasonable in this context.
With this we see that manipulation is possible. The mass media will convey the message. It is possible to create a stimulus, a message, so strong that it is “injected” (hence the name "hypodermic"): it is possible to hit the target. Between the sender and the receiver, between the stimulus and the response, there is no intermediation that prevents achieving the objectives, there is a direct cause-effect relationship, something mechanical, a void. So manipulation is possible because in the face of the enormous power of the mass media there is no element of resistance.
Telegraph model
On the other hand, Lasswell proposed the so-called telegraph model, which would represent in many aspects an evolution of the hypodermic theory, in which he presents a description of the communication situation according to "< i>who says what to who why channel and with what effect" (sender-message-receiver-channel-effect). Although this model represents a refinement of the hypodermic theory, its fundamental principles (asymmetry of roles between sender, which is active, and receiver, which is passive; tendency to unidirectionality or univocality; message understood as a series of predesigned and preconceived content) still stand.
Mathematical models
Later, in the 1940s, the mathematical theory of communication by Claude E. Shannon and Warren Weaver was presented, which marked the establishment of functionalist theory. This mathematical theory of communication, recognized as the origin of information theory, identifies for the first time the mediations between sender and receiver, taking into account the decisive role of technological communication devices. That is, with this theory the initial scheme (E-R) would be more complex.
Main contributions of the theory

The hypodermic needle theory is about:
- The form on “How to transmit a message or information to the masses”. Based on this theory, we can have a clear idea of how to convey that message, what words we should use, how we should address, what and how we should say.
- The novelty of the phenomenon of mass communications and the connection of the phenomenon with the fatal dictatorial experiences of the historical period between 1920 and 1930.
- The effect of “manipulation” produced by the media in a mass society.
Criticisms of the hypodermic theory
The theorists who define the hypodermic theory consider an isolated individual, but they know that each individual is not truly isolated: the differences of a heterogeneous group are overcome to create a unity. The power of the media is so strong that no other circumstance can provoke the response that this model achieves.
These theorists of the 20th century raise the problem produced by an enormous radical change, something that other scholars in the century XIX. In the old way of functioning, informal relationships made it easy to empathize and relate to others. However, in mass society that is very difficult. In the context of World War I, propaganda was used to convince the individual to love the country and hate the rest of the world: “hammer and anvil of social solidarity” (Lasswell). Fascism and Nazism used a bombardment of propaganda so that the messages entered directly into the skin of the individual and had an effect on them. Seeing its effects in World War I, it was used by fascist and Nazi parties and thus they rose to power. The success of propaganda lies in creating the conviction that if a message is articulated in a certain way, the desired effect will be obtained: that is manipulation. However, Lazarsfeld makes another interpretation: he says that the effect is not so clear, what is desired is not achieved.
In reality the individual is not so isolated. An abstraction is made of that individual, but other elements that are located in the space between the sender and the receiver, between the stimulus and the response, must be taken into account: there is no vacuum. The message is not injected directly into the vein. This space is full of elements: social, economic, psychological factors, etc. The reaction to the stimulus is not immediate or generalized (each individual belongs to a specific social group; they live in a network of relationships, friendships, economic interests, by age, by cultural level, etc.; individuals do not exist in a vacuum, but rather are conditioned by their environment) or mechanics as the hypodermic theory says. This remains a very simple theory, although at the time in history in which it occurred it completely fit.
Later developments
From the idea that the media have their limits, the theory of limited effects arises, from another perspective and without the intention of questioning the hypodermic theory. If the hypodermic theory takes as its starting point that there are certain reactions identical to all individuals when faced with the same messages constructed to produce certain effects, the new theories focus on the limited effects of the media.
Later, critical theory will emerge, which encompasses the Frankfurt School, Political Economy and Cultural Studies, the three theories that judge the situation of the media. These three currents have a Marxist influence and speak of late capitalism. The phrase "hypodermic needle" is intended to give a mental image of a direct, strategic, planned infusion of a message to an individual. But the more the search methodology developed, the clearer it became that the media was selectively influencing people.
The most famous incident, commonly cited as an example of the hypodermic needle model, was the radio broadcast of The War of the Worlds in 1938 and the subsequent panic reaction among the American mass audience. However, the incident actually sparked the research movement, led by Paul Lazarsfeld and Herta Herzog, which would disprove the magic bullet or hypodermic needle theory when Hadley Cantril showed that reactions to the transmission were, in fact, diverse and, in large quantities, determined by attributes of the situation in which the audience found themselves.
Lazarsfeld disapproved of the "magic bullet theory" and the "hypodermic needle models" through elective studies in 'The People's Choice'. Lazarsfeld and his colleagues conducted the study through research during the election of Franklin D. Roosevelt in 1940. The study was conducted to determine voting patterns and the relationship between the media and political power. Lazarsfeld found that the majority of the public remained untouched by the propaganda surrounding Roosevelt's campaign. On the other hand, interpersonal relationships were shown to have greater influence than the media. Lazarsfeld therefore concluded that the campaign's effects were not so powerful as to be considered complete persuasion to a 'helpless audience', an acclaim that the magic bullet, the hypodermic needle, and Lasswell affirmed. These new findings also suggested that the public can select which messages will affect them.
Lazarsfeld's unmasking of these communication models provided a path for new ideas about the effects that the media have on their audiences. Lazarsfeld introduced the idea of the two-step model in 1944. Elihu Katz contributed to the model in 1955 through studies and publications. The two-step model assumes that ideas flow from the mass media to the opinion of leaders, who in turn they transmit it to a large audience. They considered that the media message was transmitted through the opinion of leaders. Opinion leaders are categorized as individuals with the best understanding of media content and also as those with the greatest access to media. These leaders, at their core, take information from the media and explain and disseminate it to other people.
Thus, the two-step model and other communication theories suggest that the media no longer has a direct influence on viewers. Instead, interpersonal connections, and even selective exposure, play a greater role in influencing audiences in the modern era.