Study selection and characteristics
The electronic literature search identified 5,072 records. After the removal of 1,291 duplicates, 3,781 records remained. Subsequently, 3,676 records were removed after reviewing titles and abstracts, as they did not contain data on barriers to condom use among MSM. We further screened all 105 full-text articles and identified 39 articles for inclusion in the synthesis (Figure 1).
The included studies (N = 39) were conducted between 1994 and 2021. Most studies (82%) were conducted in upper-middle and high-income countries. Thirty-five studies (90%) employed a qualitative design while four (10%) used a mixed method approach. Data were typically collected using in-depth semi-structured interviews (82%), and 10% of the studies used focus group discussion. Sample size varied from 12 to 960. Detailed characteristics of the studies are described in Table 3.
Quality of the studies
All 39 studies met the cutoff of the quality assessment, which was mentioned in the Methods section and were thus included in the review (Table 2).
A total of 423 original findings relevant to condom use barriers were extracted (S1). Thematic analysis of the original findings produced six synthesized themes, which were classified into three levels according to the Social-ecology Model. Physical discomfort, lack of HIV/STI-related knowledge, substance use and psychological factors were the individual-level barriers; condom stigma, including regarding using condom as symbols of distrust, HIV/ STIs prevention, violating traditional cognition of sex, and embarrassing topic were interpersonal-level barriers; socioeconomic and situational factors, including situational unavailability, unaffordability of condoms, and power imbalance in the relationship were environmental/ structural-level barriers. (Figure 2).
Domain 1: Individual-level barriers
Thirty-two studies indicated that physical discomfort diminished consistent condom use (Table 4). Specifically, physical pain was a very common reason for not using condoms.
“Condoms are not bad, but the problem is when used for more than a minute, they tend to get dry; it starts hurting and can even cause bruises. It is good to use a condom for a few minutes and then get a new one.” (Musinguzi et al., 2015, P. 5) 
Reducing sexual pleasure was another common complain reported in 29 studies (S 1). MSM complained that condoms reduced physical sensation and diminished sexual pleasure. In order to avoid reducing sexual pleasure, delaying ejaculation, and diminishing their capabilities or sensitivity, MSM preferred not to use condoms during intercourse.
“My opinion is that men do not like to use condoms because they take away the pleasure of the actual flesh.” (Harawa et al., 2006, P. 5) 
Lack of HIV/STI-related knowledge
The findings from 25 studies (Table 4) suggested that some MSM were unclear about the necessity of condom use to prevent HIV and other STIs. Some MSM knew very little about the exact prevalence of HIV among MSM and believed it could not happen to them. Owing to a gap in sexual education and incorrect knowledge of HIV/STIs and condoms, nearly one-third of MSM were suspicious about condoms. Nine studies illustrated that as a result of inaccurate knowledge, MSM had developed their own ways to prevent HIV infection.
“So, I asked him why he agreed not to use a condom, and he told me that he just went to the toilet and took the sperms out afterwards. Actually, I also used to think that sex between men is safer since you can remove the sperms afterwards. I used to believe that until a friend told me that this is not the case.” (Moen et al., 2013, P. 11) 
Nineteen studies reported substance use as a barrier to condom use (Table 4). Intoxication and the effect of drugs including rush poppers, methamphetamine and heroin made respondents lose their self-control and decision-making capacity with regard to condom use.
“I think that...the reason most men don’t use condoms is that they are either intoxicated or on some type of drug. Caught up in the heat of the moment, they lose self-control and don’t stop to think (whether they should use condoms or not).” (Harawa et al., 2006, P. 6) 
Sixteen studies showed that psychological factors, including “fluke thinking”, negative emotions, and a vengeful perspective, contributed to condom-less sex (Table 4).
Eight studies demonstrated that “fluke thinking” was a significant factor negatively affecting condom use (Table 4). The fluke thinking tent to ignore the essence of things, act according to their needs and preferences, and believe that everything would go well as they wish . Although some MSM were aware of the risk of HIV/STIs, they believed that it could not happen to them.
“Although I have heard about the seriousness of HIV, I never thought I would be unlucky enough to be infected. Although I was worried, there was still a fluke mind for myself. I thought I could get away with it.” (Zou, 2008, P. 38) 
In seven studies, participants stated that their negative emotions were an important factor in risk-taking behavior. Bad moods, negative emotions, and daily pressure were regarded as barriers to safe sex, mainly owing to low self-esteem because of their sexual minority identities (Table 4).
“When my self-esteem is down...or if I’m depressed and just sort of, you know, feeling downtrodden by the world…it’s just, I...get into that ‘I don’t care’ mode (even without condoms).” (Adam et al., 2010, P. 5) 
Although not common, three studies demonstrated that MSM decided not to use condoms from a vengeful perspective, because they had been unexpectedly infected with HIV (Table 4).
“A person could feel, ‘Someone didn’t tell me they had a disease, so I caught it from them. So now, I’m going to give it to everybody I can.’ You know?” (Harawa et al., 2010, P. 13) 
Domain 2: Interpersonal-level barriers
Nearly all included studies (n = 35, Table 4) implied that condom stigma had a negative influence on condom use among MSM. Condom stigma refers to any taboos or misbeliefs about condom use or feeling ashamed or embarrassed to talk about using condoms. This was demonstrated through four sub-themes.
A symbol of distrust
Thirty studies indicated that concerns regarding trust and loyalty were the primary reason for non-use of condoms (Table 4). Unprotected anal intercourse was usually interpreted as a primary sign of trust and intimacy. Proposing condom use during intercourse aroused suspicions about disloyalty.
“It is based on respect, affirmation, and trust for your partner. Let’s suppose you want to be his boyfriend, and if you used a condom or required him to use one, it sends the message that you do not trust him. It is like an insult.” (Li et al., 2016, P. 7) 
Especially, having a regular sexual partner or being in a monogamous relationship were reasons not to use condoms. Participants viewed sexual monogamy as a buffer against the risk of HIV/STI acquisition within the relationship, and condom use was seen as an indicator of an inferior relationship.
“Why didn’t I wear a condom? Because I was either in a committed relationship with that person or had known that person long enough not to question him when he told me about his sexual past.” (Mustanski et al., 2014, P. 6) 
A symbol of HIV/STIs prevention
Twenty-nine studies indicated that MSM usually felt that condoms are solely for HIV/STIs prevention (Table 4). In other words, once MSM believed their partners were “safe” (without HIV infection), they no longer used condoms. On the contrary, initiating condom use automatically brought thoughts of HIV-related risk to the fore. Therefore, condoms served as a reminder of the possibility of HIV/STIs.
“It’s expected, routine, not to use a condom, because if we did, it would imply that one of us was infected or had sex outside the relationship.” (Boulton et al., 2010, P. 7-8) 
Nine studies further showed that MSM might use some techniques to assess their partners’ health to avoid the embarrassment of talking about HIV or using condoms. These techniques included observing their partner’s physical conditions (such as physical appearance), assessing their partner’s living situation, and checking their partner’s sexual history. They could also adopt the strategy of “sero-positioning” or “serosorting” (according to the HIV serostatus and/or sex role)  to decide whether to use condoms.
“I went to his home. It was a big apartment. We didn’t use condoms because I felt that he would not be an unsanitary person, and his body condition was healthy.” (Li et al., 2010, P. 5) 
Treatment optimism contributed to HIV-related high-risk behaviors as well. Given the availability of highly effective antiretroviral treatment, HIV has come to be regarded as a treatable chronic disease. Some MSM no longer had a fear of HIV and therefore might expose themselves to the risk of infection in condomless sex.
“Most people are aware of the risk factors for HIV, including not using condoms. I know people who think that HIV medication will fix things. There are a lot of gay men who think that HIV is curable, and because of that [they] take risks and don’t use condoms.” (Neville et al., 2016, P. 14) 
A symbol of violating the traditional cognition of sexual intercourse
Twelve studies reported that MSM usually hold the traditional cognition of sexual intercourse and believe that using condoms is a violation of its true purpose (Table 4). In some settings, they believed that s sexual intercourse is a symbol of “true love” and must involve direct genital contact; this is known as “rouyu” (desire of the flesh) or “bare sex.” There is a belief that during intercourse, partners should exchange body fluids. Based on this traditional cognition, condom use was deemed as violating the true meaning of human intercourse.
“At its root, love is direct flesh-to-flesh contact; that’s so-called ‘rouyu.’” Two lovers should blend in with each other.” (Li et al., 2010, P. 3) 
A symbol of an embarrassing topic
Fourteen studies showed that MSM felt embarrassed to suggest using a condom or even to initiate the discussion regarding condom use (Table 4). In some situations, although they tried to initiate a condom-related discussion, miscommunication led to awkwardness. Furthermore, buying condoms was a huge challenge, especially for young MSM. They felt ashamed to go to the store to buy condoms and did not feel smart enough as they could not determine the kind of condoms to get. They complained that cashiers gave them dirty looks because of their young appearance. Some unmarried men said they felt embarrassed to carry condoms and feared discovery by their parents or others.
“For example, I would be extremely embarrassed to ask for them (condoms), and wouldn’t even know where to get them (I think they’re sold in vending machines and pharmacies). Also, some [people] don’t know how to use them properly and would feel awkward to use them.” (Mustanski et al., 2014, P. 6) 
Domain 3: Environmental/ structural-level barriers
Thirty-one studies revealed that socioeconomic and situational factors were an insurmountable obstacle to consistent condom use (Table 4). Socioeconomic and situational factors were spread across three sub-themes: situational unavailability of condoms, unaffordability of condoms, and power imbalance in the relationship.
Situational unavailability of condoms
Evidence of situational unavailability was identified in 25 studies (Table 4). In five studies, participants experienced unplanned sex with no condom at hand. Furthermore, the “heat of the moment,” “not enough condoms,” and “unavailability of appropriately sized condoms” also contributed to the low rate of consistent condom use.
“I don’t carry condoms with me but if the other person has them, I don’t resist using them. But I know that others also don’t carry condoms with them so then most of the time we have sex without condoms.” (Chakrapani et al., 2013, P. 7) 
Unaffordability of condoms
Fifteen studies reported that despite being aware of the benefits, some MSM, particularly those who were homeless, could not afford condoms, whether of the regular type or of particularly good quality (Table 4). In some studies, MSM could get free condoms, but most of them complained that these were of poor quality, and some even experienced condom breakage or slippage and other quality deficits.
“I never used condoms because I didn’t have money to buy them or lacked both money and place to acquire them.” (Musinguzi et al., 2015, P. 5 ) 
Power imbalance in the relationship
In eight studies, there were imbalances in participants’ relationship power dynamics and sexual decision-making (Table 4). Some explained that they lacked the ability to put their point across, while others experienced sexual abuse and were forced to have unprotected intercourse. Moreover, male sexual workers who served male clients would engage in unprotected sex to earn more money.
“I don’t want it (not to use condoms), but if he gives more money, I think it’s OK.” (Kong, 2008, P. 3)