The Incredible Hulk and Sensational She-Hulk are iconic green goliaths of the Marvel comic-book and cinematic universe. Marvelous fiction transformed the scientist Bruce Banner and his cousin Jennifer Walters into these powerful green counterparts. Without a Hulk smash to separate the plausible from the sensational exploits of these superheroes, the power of the “atomic farce microscope” is applied to discern the credible from the incredible. The molecular wonders of pigments, hormones, and polymers are revealed to account for green skin, strength, and untearable undergarments concealing super-human prowess.

 

1 The Marvel Universe’s Incredible Hulk and Sensational She-Hulk

In May 1962, a green giant, The Hulk, appeared in a comic book series for the first time. The Hulk combined elements of Mary Shelley’s Frankenstein and Robert Louis Stevenson’s Dr. Jekyll and Mr. Hyde. Ignoring the imminent countdown to the detonation of the world’s first gamma bomb, government scientist Bruce Banner leaps from the safety of the bunker and sprints into the desert to rescue a waltzing teenager. Heroically pushing the adolescent into a nearby trench, Banner takes the brunt of the gamma explosion head-on. Miraculously, the mild-mannered scientist defeats death. Instead, Banner (5’9”/128 lbs or 175 cm/58 kg) is whammed by his anger, which now turns him into a gigantic monster known as the Hulk (6’9”/970 lbs or 206 cm/440 kg) in the comic book The Incredible Hulk #1 and comic history thereafter.

In February 1980, a feminine counterpart of the Hulk emerges in the pages of the comic book Savage She-Hulk #1. Attorney Jennifer Walters is injured and receives an emergency blood transfusion from her cousin, Bruce Banner. Walters acquires a milder version of the Hulk condition. She becomes a large, powerful green-hued version of herself but retains most of her personality, intelligence, and emotional control. Like Hulk, She-Hulk can become stronger if enraged. In later comic issues, She-Hulk’s transformation becomes permanent.

The origin of the Incredible Hulk owes homage to the imagination of the dynamic duo of writer Stan Lee and penciler Jack Kirby, who breathed life into the Marvel Comics superhero. A successful television series run of The Incredible Hulk (1977–1982) later inspired Marvel to launch the monthly comic book series She-Hulk, who was designed by artist John Buscema and writer Stan Lee. Lee, however, penned only the first issue before leaving Marvel until his return in 1992.

The gigantic success of the Hulk can be demonstrated by the sale of a rare copy of his first comic book appearance for almost half a million dollars in January 2022 [1]. Accruing a billion dollars from seven live-action blockbuster films since 2003, The Hulk appears a mainstay of contemporary culture bounding in animated movies, toys, and comic book series. Furthermore, She-Hulk is due to debut her own live-action TV series on Disney+ in 2022.

As fictional superheroes, the Hulks have origins and powers due to biological transformations and technological advancements beyond the credible scope of modern science. These products of a herculean imagination defy the limits of scientific principles. In the vein of distilling scientific notions emanating from Thor’s hammer [2], Iron Man’s armor [3], and Captain America’s serum [4], however, the characteristics of the Hulks’ color, strength, and underpants, all offer opportunities to learn about actual wonders of the natural world and original technical accomplishments.

 

2 Green Pigmentation

The Hulks are iconic green monsters. Their skin is green. They bleed green. Even their feces are green. Originally, deathly grey skin was envisioned for the first printing of the Incredible Hulk. However, the color grey proved more ungovernable than the muscle-bound giant, whose comic-book image bounced erratically off the presses in a spectrum of shades from dull pale smoke to striking dark ash. Faced with difficulties calibrating shades of grey, Lee and Kirby opted for a reproducible tone of green [5]. Contingent on the venue, grey, green, and even red Hulks and She-Hulks have since stomped across comic-book pages.

 

2.1 Green Skin

Skin color is usually determined by a balance of different classes of pigments such as melanins, carotenoids, and hemoglobulin derivatives [6]. In the oxygen-carrying blood protein hemoglobin, the porphyrin pigment heme (see Fig. 1) changes color from red to blue contingent on oxygenation. Grey skin is often a symptom of a lack of oxygenated blood due to various conditions such as choking, renal failure, congestive heart disease, or late-stage cancer [7]. Exogenous pigments have accounted for green pigmentation in certain patients who had absorbed tube-feeding dyes. Distinctive full-body green skin was observed in a 67-year-old woman whose yellow jaundice blended with brilliant blue food coloring (FD & C Blue No. 1, see Fig. 2) from tube feedings [8]. “Green sickness”, or chlorosis from the ancient Greek word “chloros” meaning “pale green”, describes patients with hypochromic anemia and often a distinct skin tinge due to the paling of red blood cells from reduced concentrations of hemoglobin [9].

 

Figure 1. Chemical structures of natural pigments found in bodily fluids: the heme group found in normal hemoglobin; biliverdin, a green pigment product of heme catabolism; sulfhemoglobin, a green sulfur-containing heme pigment.

 

Gamma radiation is credited for the Hulk’s green glow, but has never actually been reported to turn skin green. Green-glowing animals have been genetically engineered by the introduction and expression of the gene for the Green Fluorescent Protein (GFP) and observed under blue to ultraviolet light. Alba, a green-fluorescent rabbit, was brought to public attention in 2000 through the collaboration of French geneticist Louis-Marie Houdebine and artist Eduardo Kac [10]. Similarly, such techniques have been used to produce genetically modified mice, pigs, cats, dogs, monkeys, and fish [11–16] that fluoresce under blue to UV light. GloFish, fluorescent zebrafish, were invented with the perceived use of detecting pollution in waterways, but are now commonly sold in pet shops. In a similar manner as Grey, Green and Red Hulks have emerged from diverse plotlines, red, blue, and cyan GloFish have arrived via the application of different fluorescent proteins.

 

Figure 2. Blue food coloring FD & C Blue No.1, commonly added to tube feeding formulas to help monitor for pulmonary aspiration.

 

2.2 Green Blood

Green blood has flowed respectively from Grey and Green Hulks [17,18] during fights with Wolverine. Gory green blood may slide past the Comics Code Authority (CCA) censorship boards more easily than the red counterpart which has bled from Hulks on less gruesome occasions. Green blood does flow in a genus of skink lizards due to an excess buildup of the bile pigment biliverdin (see Fig. 1) [19,20]. Green blood has also been observed in humans suffering from sulfhemoglobinemia [21], a rare condition in which the heme pigment in hemoglobin is bound irreversibly to sulfur (see Fig. 1) [22]. The resulting sulfhemoglobin (SulfHb) causes cyanosis, a bluish tint, even at low concentrations in blood.

 

2.3 Green Feces

Hulk has discharged green feces [23]. The colors of such excretions may be due to pigments from the food he eats, such as chlorophyll in spinach and broccoli, green food coloring from flavored drink mixes, ice pops, and birthday-cake icing, even iron supplements [24]. Alternatively, the incomplete breakdown of bile in food moving rapidly through the intestines may turn his stools green. Speculating on the feces of She-Hulk, the commonly known side effect of birth control containing medroxyprogesterone may color them green [25].

On a lighter tone, the German shepherd “Dog-Hulk” was born with light-green fur in a healthy litter with seven white puppies. According to the veterinarian, the rare green puppy may likely have been dyed in the amniotic sac with meconium, the earliest stool of infant mammals. After a few weeks of bathing, Dog-Hulk’s green coloration faded away [26,27].

 

3 Super Strength

Pound for pound, the strongest living creature on Earth is the Gonorrhea bacterium, which can pull up to one hundred thousand times its own body weight [28]. In spite of being a scale bigger, the second strongest creature, the oribatid mite, can lift around one thousand times its body weight [29].

In life-threatening situations, certain humans have lifted dozens of times their own weight employing so-called “hysterical strength” [30]. Reports of feats by people empowered with hysterical strength include saving relatives by lifting automobiles, pushing away fallen boulders, and fighting off polar bears [31–33]. Artist Jack Kirby claimed seeing a woman lift a car off her baby as his inspiration for creating the Hulk [34]. The fight-or-flight hormone adrenaline can boost muscle strength, priming the body for emergency action by speeding up heart rate, lung capacity, blood vessel dilation, and nutrient release [35]. The “runner’s high” neuropeptide hormone endorphins can also suppress pain and boost the ability to complete arduous tasks [36].

Double-muscled pigs have been genetically engineered by mutation of the myostatin gene MSTN. By inhibiting muscle cell growth, MSTN keeps muscle size in check. Mutations of MSTN in cattle, mice, bully whippet dogs, and humans have led to muscle cell proliferation and abnormally bulky muscle fibers [37]. Myostatin-related muscle hypertrophy is a rare genetic condition characterized by reduced body fat and increased skeletal muscle size [38,39].

 

4 Stretchy Pants

The shirt-ripping, shoe-popping, clothes-tearing seven-fold expansion of Bruce Banner into the Hulk generally fails to split his signature purple shorts. She-Hulk Jennifer Walters has explained that her underwear never leaves her totally exposed in a fight because her clothes are “Protected by the Comic Code Authority (CCA)” [40]. The vehement anti-nudity attitude of the CCA has similarly kept the Hulk’s privates clothed in purple [41]. Since college, Banner has claimed to emulate Albert Einstein by buying ten identical suits—all purple—so he would not have to waste time deciding what to wear [42]. Banner is also said to wear purple pants underneath his clothes, like a regular superhero costume.

Stan Lee explained the stick-to-itiveness of the purple shorts as a gift care of Reed Richards, or Mister Fantastic, who outfitted Banner with “elastic trousers” made of the same materials used in the costumes of the Fantastic Four superhero team [43]. Elastane fibers, first synthesized by DuPont Laboratories in 1958, can stretch up to 600 % of their original length and return to their original shape numerous times before losing elasticity [44]. “Elastic” refers to “the ability of a material to resume original shape after deformation by external force.” The name and properties of elastane have stretched over the years to include Spandex, an anagram of the word “expands”, Lycra [45], Elaspan, and Dorlastan, all containing structures featuring rigid and flexible segments which enable polymer elasticity (see Fig. 3). Like the Hulk, who to a certain degree can mesh with the Avenger’s superhero team and pair up with Wolverine, elastane blends well to increase the flexibility of other fibers, such as polyester, nylon, cotton, and wool.

 

Figure 3. The chemical structure of elastane seems almost as elastic as the Hulk’s shorts, with at least two reported images [44,46].

 

In nature, spider-silk protein exhibits remarkable tensile strength, elasticity, and durability with the potential to be stronger than steel and more stretchable than rubber [47]. Synthetic spider silk, Microsilk™, has been created without harming spiders using biologically engineered yeast. Industrial quantities of the biodegradable protein-based fiber are made by the microorganisms with less environmental impact than traditional textile manufacturing [48]. Spider-silk protein contains usually random-coil, helical, and sheet contents. Like elastane, the coil and helical regions are flexible and can stretch, while the sheet portions remain relatively stable [49,50].

Recent advances in material science allowed researchers to create super stretchy, self-healing materials that can stretch up to 5,600 % [51,52]. Such novel urea functionalized poly-(dimethyl siloxane)-based elastomers (U-PDMS-Es) have potential for various applications, including artificial muscles. After damage, the rubbery polymers heal completely within 20–120 min contingent on temperature. Although such promising polymers have yet to be spun into textiles, their elastic and self-healing properties would be ideal for retaining the Hulk’s discretion under revealing adventurous conditions.

 

5 Conclusion

Green color, muscular physique, and even stretchable undergarments, all have respectively been observed in nature and the laboratory due to chemical and genetic transformations. The imagination of Stan Lee is, however, required to explain the potential of gamma-ray exposure and anger to unleash the superpowers of the Hulks. Inspired by the latter, the Human Universal Load Carrier (HULC) is being developed as a hydraulically powered exoskeleton to enable soldiers to carry loads up to 200 lbs (91 kg) with minimal strain on their body [53]. Weighing his opinion on such a heavy subject to his cousin Jennifer Walters, Bruce Banner may likely say, “Some people are good at war. I preferred science” [54].

 

Acknowledgments

The authors thank Corentin Martinage for the chemically heroic illustrations.

 

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Author Information

Yann Brouillette (Corresponding Author)
Chemistry Department, Dawson College, 3040 Sherbrooke St. W., Westmount, Quebec, Canada H3Z 1A4 ([email protected])

William D. Lubell
Département de Chimie, Université de Montréal, Complexe des Sciences, 1375 Avenue Thérèse-Lavoie-Roux Montréal, Québec H2V 0B3
([email protected])

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