## 1 Introduction  
The cough is a vital protective and defensive reflex that the body uses to remove mucus and irritants from the lower airways. On the other hand, excessive or pathologic coughing is among the most common complaints affecting the general population including both adults and children, and it usually represents one of the most frequent reasons for seeking medical consultation. It affects negatively people's quality of life, causing distress and sleep disruption. In fact, coughing often becomes worse at night because the laying position causes mucus to stagnate in the throat. Upper respiratory tract infections, also known as the common cold, and acute bronchitis are the most common causes of acute cough in adults. These conditions are characterised by acute inflammation of the mucosa associated with oedema and increased secretions and mucus production. Although the majority of acute respiratory tract infections are caused by viruses and are self-limited, a persisting cough may lead to further irritation of the oropharyngeal mucosa making it more sensitive to local irritants and starting a vicious cycle able to damage the tissue itself [1]. Moreover, inhalation of foreign irritants can trigger the sensory nerves in the upper airways and lungs causing the cough reflex. Generally, in adults and older children, a common cold tends to last about one week while a cough may persist for up to three weeks or longer [2]. On the contrary, a chronic cough may represent a key symptom of more severe conditions such as chronic obstructive pulmonary disease (COPD) or extra-pulmonary disease such as gastroesophageal reflux disease (GERD) [3]. A recent online survey found that a cough outlasted other cold symptoms in 69% of the survey respondents [4]. Adults in the United States have an average of two to three colds per year, and this number is even higher in children [5]. According to a recent survey carried out in Italy on 1251 subjects, 18.4% of respondents reported more than three episodes of cough/year with a duration ranging 10-30 days in about 20% of subjects and longer than 30 days in 7% of subjects [6]. Interestingly, 23% of subjects declared using domestic remedies for cough relief while almost 21% ask for advice from the pharmacist, or the doctor (33.4%), primarily the general practitioner [6]. _Pelargonium sidoides_, also known as African geranium, is native to South Africa and its root extract has been traditionally used to treat URTI when antibiotic use is unnecessary [7], due to its clinical effectiveness and margin of safety in different target populations including children [8,9] and teenagers [10]. A variety of potential mechanisms have been identified which provide a rational basis for its use, including moderate antagonistic effects against both viruses and bacteria. In fact, _P. sidoides_ extract may interfere with the invasion and adherence of several pathogen microorganisms such as group-A streptococci (i.e., _S. pyogenes_) to human host cells [8,11], potentially preventing bacterial superinfection [12, 13, 14]. Other hypotheses include similar effects on viral adherence [15, 16, 17]. _Pelargonium sidoides_ root extract interferes with the replication of several respiratory viruses such as seasonal influenza virus, human coronavirus, parainfluenza virus, and coxsackievirus, mainly acting indirectly by inhibition of virus attachment to the host cells and spreading whilst no direct virucidal effect is reported [18]. The extract exhibits mucolytic properties and improves cilia function in vitro, thus favouring the clearance of excess mucous and bacteria from the upper airways [19]. Moreover, _P. sidoides_ extract is able to boost the immune response to infection through the improvement of the innate immune defence, enhancement of macrophages phagocytic activity, and a positive effect on NK cells activity and oxidative burst was also shown [14].