Hot answers tagged

29

First, tattoo pigment isn't injected into cells. If you were to puncture a cell with something the size of a tattoo needle, it would die - full stop. Many cells are destroyed in the process though, mostly by tearing, which initiates the wound healing process. So what actually happens is the particles lodge in between the cells of the dermis (the layer below ...


23

You're talking about long-wave UV, or UV-A radiation. In the 80s, experts claimed that this was a safe wavelength. Protection against UV-A was not part of sunscreen in the early days. Consequently, UV-A was (and still is) used in tanning beds due to its perceived safety over UV-B. However, a lot of research has been done since. UV-A is well understood now ...


17

Rather than 'breaks' caused by high energy radiation, UV radiation causes chemical modifications of the bases ('letters') that make up DNA. There are four bases in the DNA alphabet abbreviated to A,T,G or C belonging to two classes. A & G are guanines while T & C are pyrimidines. When you have pyrimidine bases next to each other on a DNA strand, they ...


15

There are very many photochemical reactions: Up to 50–100 mutagenic reactions on DNA per second might occur in a skin cell during exposure to sunlight, but are usually corrected within seconds by photolyase reactivation or nucleotide excision repair. (That's just DNA, excluding O2 and other cell constituents) chemist ref and wiki ref Molecules that absorb ...


12

Contrary to the other answer posted, this paper shows via microscope images that the tattoo ink is in fact absorbed into cells, and forms small intracellular round granules. Electron microscopy of untreated tattoos revealed membrane-bound pigment granules, predominantly within fibroblasts and macrophages, and occasionally in mast cells. These ...


11

1) Is this plausible? It is absolutely plausible. His particular condition was called Vitiligo (as stated in your quote) and isn't that uncommon, albeit not usually as severe. Skin pigmentation expression changes over time, sometimes dramatically. 2) Is it likely to be an actual disease, or would there be so many mitigating factors that it is unlikely ...


10

Afaik the tongue is not more heat tolerant than other parts of the body, so the minimum temperature to cause burn is about drinking a beverage having 45°C temperature for a long time (more than 5 minutes). The pain threshold of tongue is around 47°C, so you will feel when it really burns. According to studies the hedonic value of coffee has a maximum by 60°...


10

With about 20 square feet of skin constantly exposed to potential irritation, itching must serve an important protective/defensive function. The "scratch reflex" (I'm not sure I would call it that) is necessary to life and limb. Itch is a major somatic sensation, along with (and different from) pain, temperature, and touch. Itch can be an acute sensation, ...


10

I will assume the hand washing you speak of involves soap. The human skin (which also covers hands) is a complex organ with an underlying system of glands. One of these is the exocrine sebaceous gland which is responsible for the production of a substance known as sebum. This substance is primarily composed of triglycerides, wax esters and other fatty ...


9

This is a normal part of the inflammatory process. Inflammation is your body's localised defensive response to tissue injury of any kind, and it is characterised by four cardinal signs- redness, swelling, heat and pain (severe inflammation involves a fifth, loss of function). Your body is performing three main processes here: Mobilisation of the body's ...


9

Note: I am not stating that moles are in general circular in shape because there are no statistical studies to conclusively state so. This answer is mostly about default circular shape of cell colonies. Moles (melanocytic naevi) are not strictly circular but generally have have a rough circular shape. Moles can have irregular shapes too and you can easily ...


9

Think of what happens when you don't wash your hair for days. It gets oily and greasy. This oil-like substance on your hair is called sebum and mainly works as a lubricant . The Sebaceous glands responsible for excreting sebum don't stop working when the hair follicles attached to them do. The result is a "shiny" head.


8

The human skin is indeed made off a number of different layers, the three most important are epidermis, dermis and hypodermis (also called subcutaneous fat), see the figure (from here) for details: All three layers can be subcategorized further, I'll only give a few details here. More can be found for example in the Wikipedia article on skin. Epidermis: ...


8

Sweat is actually odorless regardless of what type of sweat gland it comes from, of which there are two types - apocrine and eccrine. As suggested by canadianer, the odor comes from the mixture of bacteria and the resulting sweat. With regards to why your bacterial flora is so diverse is likely due to the different micro-environments found around your body. ...


8

It didn't, the basal condition for humans is dark skin, all other pigmentation patterns evolved from it. Additionally Dark skin is not monophyletic/homologous in humans, that is some darks skinned humans evolved from light skinned humans who in turn evolved from ancestral dark skinned humans, (Evolution made skin lighter then made it darker again in other ...


7

The genetics of pigmentation is relatively complicated, as the pathway for the pigmentation (regulation of the pigment production, ratio between the melanins, maturation, trafficking and distribution of the melanins from the melanocytes to other cells) is quite long and also subject to different regulations. All the mutations found to date (at least to my ...


7

Pure nicotine is a yellow colored liquid (although some sources say it's a clear liquid.) "Tar" is a complex sludge that is also yellow-brown. So it's difficult to distinguish 'nicotine stain' from a 'tar stain' based on visual inspection. Let's go to other considerations. The concept of a 'stain' implies that simple hand washing doesn't remove the ...


7

I had the same thing happen to my leg. I think it eventually went away, but it was definitely many years. I am going to go with the Tattoo answer. The way tattoos work is that Macrophages in the skin phagocytose the heavy metals in the inks. Because the heavy metals do not interact with Toll-like receptors, or any of the other pathogen receptors that ...


6

Scar tissue formation is part of the normal healing process in which fibrous material braces and pulls the wound together, in other organisms (and young mammals) this process is mild and just serves to temporarily reinforce the damaged tissue as new cells migrate in to begin replacing the missing tissue, sometimes to the point of replacing missing limbs in ...


6

There are (at least) two sides to this story. One is direct DNA damage being caused by UV-B light which happens to have photons with just the right amount of energy to interact with thymine. This has been known, and assumed not just during the 80s, but until the late 2000s to be The One major thing that causes cancer, or trouble in general (there's papers ...


5

Vitamin A: One study conducted in the 60's claims that vitamin A acid prevents formation of comedones in Acne Vulgaris [1]. Another one conducted in the 70's found no significant improvement of plantar warts when vitamin A acid was applied topically [2]. Vitamin D: Agents like calcipotriene associated with topical steroids are effective against psoriazis [3]...


5

Human skin is made up of three layers [1]: Epidermis; it contains no blood vessels; it has 5 cellular layers (starting from surface): stratum corneum stratum lucidum stratum granulosum stratum spinosum stratum germinativum Dermis; it is separated from the above by the basal membrane; made up of connective tissue (with blood vessels and nerve endings) ...


5

This depends on a lot of factors, including how you take your first sip. If you sip with air, you are altering the temperature of the liquid as you sip, as well as decreasing the volume of hot liquid in your mouth, so that the increased surface area of your exposed tongue can quickly alter the temperature of a borderline scalding liquid into a non-scalding ...


5

This is the modified answer in response to the discussion: Facts: There are warmth and cold receptors in the body at two places: The Peripheral receptors and the Central Receptors The peripheral receptors are present in skin and the central receptors in the body core at multiple sites the notable site being the hypothalamus The Temperature receptors have ...


5

This depends on a number of factors. Here are the first two that come to mind: 1) Is the cut deep enough to reach the dermis (this is the layer below the epidermis) where scar tissue will form? 2) What is your general state of health, and was there an infection at the site of the cut, which would have altered the normal healing process. Basically, not ...


5

The reason for laser hair removal/growth products not being safe for darker skin tones is the ability for darker skin tones to absorb more light from the laser than lighter skin does BEFORE the light is able to reach the depth at which the hair follicle is located. Light from lasers must pass through the epidermis where melanocytes are located before they ...


5

Short answer Humans sense temperature differences. Background (Including edits based upon comments) Because the question is "Do humans perceive temperature or heat-flux?", I will answer the answer from a psychophysical perspective, i.e., by dealing with sensory awareness. Just as with many other sensory systems, temperature sensors in the human body ...


5

It's a phenomenon called Frisson. From the wikipedia page. Frisson (French for 'shiver') is a sensation somewhat like shivering, usually caused by stimuli. It is typically expressed as an overwhelming emotional response combined with piloerection (goosebumps). Stimuli that produce a response are specific to the individual. Frisson is of short ...


5

Since there are different formulations for anti-aging creams, it would be helpful to focus on the specific compound or combination of compounds. According to a comprehensive literature review done in 2007, certain compounds (Vitamin C, alpha-hydroxy acids, Vitamin A, Vitamin B derivatives, and botanicals) have had varied success in literature ...


5

Pores don't change size; that is, the diameter of pore does not increase or decrease in hot or cold environments. Your skin, where pores are located, is not muscle but an organ so the pores don't contract or expand. Pores can become clogged with dirt, oil, and debris (make up). When pores are clogged, you are more inclined to notice which would cause the ...


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