It's a curious saying: "Cold hands, warm heart." It proposes that people whose hands are usually cold actually have kind and loving personalities. There is no counterpart as far as I can tell. That is, people with warm hands aren't reputed to have cold hearts. They're just regular folk whose body temperatures hover at the norm of 98.6 degrees F.
In 2008 researchers Lawrence Williams and John Bargh garnered some press for disbunking this saying. The study found that experiences of physical warmth activated concepts of interpersonal warmth. What is interpersonal warmth? It refers to a series of traits that we perceive in others as being favorable to us—for example, we might talk about how friendly, or helpful, or trustworthy someone might be, which helps us assess whether he is friend-material or someone who should be avoided. Exposure to physical warmth seemed to trigger behaviors to encourage these perceptions about us. So, for example, we might be more likely to share or think ahead about and plan for reciprocal behaviors. Exposure to cold seemed to help us focus our attentions more selfishly.
The warm-cold divide may be rooted in our physical experiences with these sensations. Experiences of warmth may trigger other associations we have with this sensation, which links it to psychological warmth. As an example, Williams and Bargh cited Harry Harlow's classic study with macaques where infants demonstrated a preference for a cloth surrogate mother over a wire mother who provided food. If you don't know this study, it's actually an interesting read, and you can learn more here. If you're interested, there's also a video, but be warned, it might tug at your heart a bit—Harlow's experiments have been criticized as being cruel and unethical, however, the video does not contain any explicit physical violence against the macaques. The issues are more psychological. (I also summarized the study following the video, so feel free to skip ahead.)
[Disclaimer: This video shows infant macaques being held in cages, and may be difficult for some people to watch. However, there is no sign of physical violence. And it is highly illustrative of Harlow's research.]
The short of it is that researchers presented two surrogate "mothers" to infant macaques. One was made of cloth and heated with a light bulb and the other was constructed from wire but provided food. The monkeys chose the cloth mothers for comfort and only turned to the wire mothers when driven to do so by hunger. Harlow used these findings to establish the importance of comfort from contact, particularly in the early years of life. The absence of this sort of comfort has been tied to severe developmental issues later in life. Harlow's work has been instrumental in the ways child care agencies approach and design care policies for children.
So we have these associations of comfort and safety and trust tied to warmth because our early caregivers provide these components of psychological warmth in addition to actual physical warmth (606). In the Williams and Bargh study, research participants who briefly held a hot cup of coffee, were more likely to perceive others as having warmer personality traits than participants who briefly held an iced coffee. And participants who held a hot therapeutic pad were more likely later to choose a reward that they could share with a friend than those who held a cold therapeutic pad (607).
The study pinpoints of the influence of external factors in our relationships with others. If you're exposed to cold, for example, which can be an uncomfortable state, you may be more inclined to think of yourself. It's actually pretty understandable that you want to make yourself comfortable. If you're warm, which means you are presumably comfortable (not hot and sweaty, which can be uncomfortable), you may be more receptive to thinking about others because your needs are already accounted for. So cold hands do not equate with a "warm heart," but suggests a state of discomfort that should be addressed.
But the saying maintains that people whose hands are usually cold, have warm hearts regardless. So while a temporary environmental change may impact how we perceive others and behave towards them, is the same true of someone whose experience of hot and cold remains more or less constant? That person who is cold in the heat of the summer months—you know the one I mean—is she less psychologically warm than others? Or perhaps this saying evolved to help normalize an unusual experience?
If our aversion is cold is such that it generates negative connections, it makes sense that we would want to remove people we're fond of from those associations. So "cold hands, warm heart" becomes a means of dismissing an anomaly and asserting sameness. The hot-cold assessment may be a "first-pass" judgment regarding the suitability of an individual to belong to our social networks. Williams and Bargh suggest that it may also be "an automatic and obligatory evaluation that does not require the perceiver's intent to make it" (606). Does "cold hands, warm heart" then function as a way to by-pass this initial assessment? My sense is that the phrase is used more affectionately than this context would permit—but it does perhaps serve as a way to assuage concerns about self and the psychological implications/associations with coldness.
Williams LE, & Bargh JA (2008). Experiencing physical warmth promotes interpersonal warmth. Science (New York, N.Y.), 322 (5901), 606-7 PMID: 18948544