As to whether or not the presence of an eco-label influences consumers’ sustainable purchases and their impacts, discordant results can be observed. On one hand, a pilot study, conducted in an online supermarket from van der Waal et al. (26), found that an explanatory health claim added to an explanatory sustainability claim was not effective in fostering sustainable purchases, while explanatory sustainability claim alone was even associated to lower correspondent purchases from people having low environmental attitudes. Whereas van Bussel et al. (27) found in their systematic review that price, taste, and individual health were more important for consumers than sustainability.

Nonetheless, positive results were instead found in other studies (28–35) in which the application of eco-labels changed consumer behavior, proving that eco-labels can influence the number of attributes considered when purchasing a product. More specifically, when different wordings are compared, those referring to “sustainably” or “locally” sourced products were chosen the most (32) along with “organic,” as stated in a systematic review (36), similarly to those with traffic lights (37). Eco-labels could also lead to an increased perceived quality of the product (38). Regarding other perceptions, consumers do not have a negative perception of the brands in the presence of an eco-label (39).

When buying or acquiring foods, a clear informative seal that provides easy-to-understand information (40) could trigger a choice toward more sustainable products, even for people who do not have prior information on sustainability (41), as this choice could also be partly subconscious (42). However, it must be taken into consideration that there are substantial differences among preferences between different countries, the motivations of purchase and consumers themselves, such as demographic characteristics and human and cultural values (e.g., if it is a desired attribute; if it is accepted) (43). For example, among the reasons of choosing a label, Zepeda et al. (43) found that the object itself (such as the type of label, quality, and hedonic components) was the main reason (64.4%), followed by the label source (such as the credibility, reputation) (45.5%), and then the consumer characteristics (e.g., willingness to pay, attitude toward the label, etc.) (42.1%).

Although some authors found different results (44), the tendency of the evidence is that this impact in changing consumer behavior is best observed with those who already show some degree of concern and knowledge about the impact of their consumption patterns on the environment (45), or for those who understand the eco-label clearly, as this was found to be a prerequisite of using the eco-labels (46). The sustainability knowledge plus the eco-label acted as a consistent predictor of consumers’ choice strategy (32).

Eco-labeling could also have long-term impacts over consumers. For instance, in the United States, a change in consumption behavior was seen with the introduction of this new category of information on food products. One of the most visible examples was in 1990 with the introduction of the “dolphin-safe” label on tuna cans. The market share of canned tuna companies certified as “protectors of dolphins” had a constant growth reaching more than 90% of the market share, an effect that was maintained over time (28). This accounts for a long-term impact that labels can have on the various market players in terms of sustainability.

One effect that certification of meeting a sustainability standard can produce is that producers increase the price of said product, either because it effectively makes the production of that good more expensive, or because of the possibility of classifying said good as “premium” in relation to other similar ones that do not have the certification. However, a studied carried out in Japan and the United Kingdom found no distortionary impact on consumer preferences for eco-labels (47).

Producers may invest in innovation to meet the new standards and thus become certified. For example, in the case of the “dolphin safe” label, it was plausible that the price of tuna would increase as a result of the new production techniques, and this would particularly affect the lowest income households, which may not be willing or have the resources to pay for the “dolphin safe” products, which could imply a redistribution of welfare from low-income households to high-income households (10). If standards are so strict that production costs exceed the prices consumers are willing to pay, consumers will seek products with lower standards, so producers will not continue innovation efforts, making such high standards lose meaning.

Regarding consumer’s willingness to pay for a labeled-product, heterogenous results have been obtained, as some studies found no intention, or intention only if accompanied with discounts, to a higher price for them (48). On the contrary, both a meta-analysis (49) and original articles (50–53) found that consumers were willing to pay a premium price, even though the eco-product was not the preferred one according to taste (54). This could be due to the hypothetical scenarios, where no real money is on the line, as it has been reported that consumers overestimate the willingness to pay on this type of studies (55).

Higher prices may be the case for organic labels, as confirmed by meta-analyses and/or systematic reviews (24, 49, 56). The willingness to pay seems to be more associated with higher label penetration into market than to the certification transparency itself (57). However, familiarity with the label seems not to be the case for China, as Zhu et al. (58) found that Chinese consumers’ willingness to pay a higher price was only if the Chinese organic label was accompanied with one from abroad (e.g., EU organic). However, it is important to say that a study found that consumers were willing to pay up to 23% higher prices for familiar tagged (unverified claims) products compared to an existing certified eco-label such as Marine Stewardship Council (MSC) (59).

Finally, cross-cultural differences are also an interesting point to take into account. For example, one study compared the same products between German and Canadian consumers (48). The authors found that German consumers prefer more sustainable products than Canadians, influencing also the willingness to pay. In general, richer and more populated countries are prone to consider environmental issues, however, there are some very low-income countries also concerned about sustainability (14). Therefore, cultural preferences also influence the willingness to pay and the importance level of the sustainability attribute of food.

It is important to consider that transformative effects are reached if eco-labeling is situated in a legal and institutional framework that seeks to move from less sustainable ways of production and consumption toward others that are more sustainable and accessible both physically and economically. A review also suggested that producers must be involved in those changes as it is expected to impact the manufacturing process (60).

A direct effect derived from the implementation of labeling is related to the transformation in product elaboration. As green consumers prefer more sustainable products, there is an incentive for producers to adopt new, more innovative and sustainable practices to satisfy these consumers. This is not only true for big companies, but also for farmers and producers, as they also prefer having an eco-label, however, they were mostly worried about long-term health effects than for increasing exports or other aspects (61). When establishing a type of certificate or eco-label, some producers are forced to reveal negative characteristics of their products. Therefore, it is plausible that producers decide to change the characteristics of their product during the production process to meet the standards of the implemented certificate and not risk losing customers-in the short term-and market share and revenue-in the mid and long term (10).

Likewise, this may lead to more producers wanting to gather information on the environmental characteristics of their products to be more competitive, which could lead to further innovation and more sustainable solutions. This process could become a real challenge when measuring the environmental footprint, which could in turn retract producers of adhering to the label (62). There has been reluctance from retailers to include these type of labels, even though it has not been shown to result in negative consumer side perceptions (39), but in some cases it has not resulted in increased profits for producers either (63).

Even though eco-labels are more present in wealthier countries (14), the following evidence could be applied for the institutional framework in any country. Regulated and transparent certifying entities could help strengthen labeling through inspections, certifications and fines. As stated in the first section, consumer’s trust in the label is fundamental for behavioral change. When doing so, it is important to consider interaction among stakeholders, as they could be a barrier into this implementation due to lack of agreement (64).

It was suggested that consumers’ acceptance of sustainability could differ by whether consumers trust or distrust the label information (48). Differences between countries could be attributable to trust in the public agencies, thus altering the impact of the label. Labels that are not consistent with achievable standards, inspections, certification services and sanctions could not be effective, and could even generate major market disruptions (10). However, a review suggested this could also be a result of inconsistency in reference values and indicators or dimensions considered; therefore, the same profiling models should be used (65). Even though there are some doubts about the transparency of some certification processes, e.g., of sustainable fisheries, a study found that products certified had between 3 and 5 times less probabilities to have harmful practices (23); lack of credibility (46, 66, 67); unfamiliarity (68); confusion regarding the content of the label since it affects its effectiveness (10). Along with trust in the label (66), being provided with clear and meaningful information on eco-labels is particularly relevant for consumers as they may misunderstand it (69, 70). According to the authors’ explanation, the importance of organic food to consumers could be partially explained by higher understanding of consumers to this label in comparison to others (71). This is further corroborated by Kaczorowska et al. (68), who suggested that unfamiliar logos have less probability of being used. In general, a higher understanding of sustainability standards leads to a more frequent use of the labels for consumers’ decisions. Thus, ease of understanding is a prerequisite for the functionality of any label. One possibility is doing self-explanatory labels as these reach higher understanding among consumers (71). In addition, educational campaigns that allow the general public to correctly understand eco-labeling, its meaning, its objectives and its relevance to the environment (70) are required. Failure to do so could damage consumer confidence in the system. If the education campaigns about the new certificate are appropriate and widely disseminated, a greater impact can be generated.

The design of the certificate or eco-label is key for it to produce the expected effects, both for consumers and for the whole system. Simple and clear graphic designs are more effective in influencing the risk perception and consumer behavior changes than any information table with text or numbers (72, 73). However, a recent systematic review and meta-analysis concluded that despite different eco-label formats, all lead to selection and purchase of more sustainable products (74).

It is also necessary to take into account the influence produced by the colors of the labels as they can lead consumers to be confused, as it is understood that products with a green label are healthier and more sustainable (75). In fact, a recent review found that there was more effectiveness in traffic-light systems when they showed an “alert” (e.g., red color) rather than the green one on purchase intention or purchase behavior (73).

Another relevant aspect is the location of the stamp, certificate, or information. The evidence shows that the frontal and central location of the container or package produces better impacts and, in short, causes a greater reduction of the environmental impact because consumers choose more sustainable products (73). This position could lower the unawareness risk, as this is also a concern. For example, in a Greek study up to 26% of the participants did not notice the content of the label (53). Even worse results were found in Italy, where up to 75% of consumers did not notice the label (76). Therefore, educational policies are necessary for the label to be understood and noticed (76).

As there is an ecosystem of labels on foods, it is a common suggestion having different categories of labels together, for example, nutritional and environmental. But this suggestion has discrepancy on its impacts over the consumer (26, 72), as it induces trade-offs between both (73). In addition, consumers have been found to limit cognitive ability, and to be distracted or dissuaded from considering many labels (41), and thus losing effect of the label (42). For example, a recent study in France showed that there is a decrease in the impact of adding more scores (25). However, evidence also shows that consumers tend to look for labels that have value to them, therefore having more labels do not necessarily mean a higher value for all consumers (77).

It was found in Germany that consumers even preferred a combination of labels, as one label did not dimmish the effect of the other, and consumers handled both labels being able to face contradictory information and trade-offs (67). For example, having two different indicators allows this differentiation to be made (78) and also to compare them (78). This is especially relevant when taking into consideration that the familiarity and trust are core to the label’s impact, and that consumers tend to be skeptical about unfamiliar and vague labels (77).

To establish a robust labeling or certification system, it is essential to choose between a binary seal (i.e., the product either meets the standard or not) or a label that considers a gradual score (i.e., allowing for gradation and differentiation by percentages). For example, a study conducted in the United States showed that an eco-label or certification is less useful and had lower importance score than a sustainability tag (in the study defined as a word, phrase or simple picture either on the promotion or in the product itself) (59). Thus, simplicity could be even more important than the process of certification itself.

Finally, socio-demographic characteristics, such as gender, age, and educational level, have been found to differently affect expectations regarding the information related to environmental sustainability, as investigated for food packaging by Chirilli et al. (79). For example, women are more environmentally conscious, while younger and more educated consumers are more aware of labels and environmental sustainability, respectively, than their counterparts (79).