29
votes
Accepted
Why do tattoos persist if body cells are regularly renewed?
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, ...
- 1,763
24
votes
Accepted
Can UV radiation be safe for the skin?
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-...
- 6,152
17
votes
Why does UV radiation from the Sun cause skin cancer?
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,...
- 1,415
15
votes
Why does UV radiation from the Sun cause skin cancer?
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 ...
- 9,322
12
votes
Why do tattoos persist if body cells are regularly renewed?
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 ...
- 9,434
10
votes
Why are bald heads so "shiny"?
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 ...
10
votes
Why hand washing causes skin to dry?
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 ...
- 557
9
votes
Accepted
Why are skin moles (pigmented spots) circular in shape?
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 ...
- 35.2k
9
votes
Why did humans evolved the scratch reflex?
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) ...
- 24.7k
8
votes
Accepted
Why the smell of sweat greatly varies across the body?
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 ...
- 183
8
votes
Accepted
Why did evolution make people's skin dark?
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 ...
- 13.9k
7
votes
Accepted
My hand was stabbed with a pencil tip 10 years ago - why is the graphite still visible?
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 ...
- 4,975
7
votes
Accepted
How does a smoker's finger or mustache get yellowish by nicotine?
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 '...
- 1,457
7
votes
Accepted
Skin color explanation?
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 ...
- 51.2k
7
votes
Can UV radiation be safe for the skin?
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 ...
- 259
6
votes
Can anti-aging cream work?
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 ...
- 636
6
votes
Accepted
If cells regularly renew, why do we have scars?
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 ...
- 13.9k
5
votes
Why can good music raise goosebumps?
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 ...
- 151
5
votes
Accepted
Do sweat pores change diameter?
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 ...
- 2,177
5
votes
How does a smoker's finger or mustache get yellowish by nicotine?
Short answer
Tar deposition is the cause of the yellow cigarette stains.
Background
Both tar and nicotine cause yellow to brown staining. Although nicotine itself is colorless/white, it turns yellow ...
- 52.2k
5
votes
Accepted
Can pathogens enter the bloodstream if the epidermis has been scraped off?
Our epidermis is the first line defence against natural infections; it is also a part of the innate immune system. This is due to
it contains a layer of dead cells that separates the living cells of ...
- 513
5
votes
Do goosebumps always appear in the same spots on the skin?
Goosebumps are caused by the contraction of the arrector pili muscles, which are attached to hair follicles. Accordingly, they appear at the same spots on one's body every time.
- 151
5
votes
Accepted
How and why do skin tags develop?
Given that skin tags are considered benign, it doesn't surprise me to find very little published research focusing on them. It's unlikely that much grant money exists to answer questions about them.
...
- 1,879
5
votes
Accepted
Can viruses pass through sweat pores?
'Pore' is a confusing term. Sweat is produced in sweat glands, and subsequently excreted through a duct, as indicated in the image below (sudoriferous ~).
In short, viruses cannot enter the body ...
- 168
5
votes
Accepted
How is sebum secretion regulated?
Nice question! Unfortunately, the complete list of pathways involved in regulation of sebum production and secretion rate by sebaceous glands are not understood yet (Picardo et al, 2009). However, we ...
- 14.1k
5
votes
Why sun rays don't burn our skin?
The reason that UV light causes sunburn, while normal light does not, is not founded in the energy carried by single photon. As stated on wikipedia:
Importantly, both sunburn and the increase in ...
- 4,371
5
votes
Why sun rays don't burn our skin?
Proteins and DNA absorb light in the UV spectrum (both UVA and UVB) because that is the energy level at which pi electrons in the aromatic rings get excited (nucleotides and aromatic amino acids have ...
- 3,068
5
votes
Accepted
Why does UVA penetrate deeper than UVB, though it's weaker?
Our skin contains quite a lot of water and I think this is answers the question: The absorption of UV light by this water goes drastically up when you shift to shorter wavelengts with a minimum ...
- 51.2k
5
votes
Is there any difference between fascia and skin ?Are both the different names of the same thing?
The superficial fascia is the lowermost layer of the skin found in nearly all parts of the body and it usually blends with the reticular region of the dermis. But that doesn't mean it's a part of the ...
5
votes
Why does hair turn white but not skin?
The answer to this question has its reason in the hair cycle. Our hair goes through a cycle of growth. At the end of this cycle, the cells in the hair follicle die and have to be replenished before a ...
- 51.2k
Only top scored, non community-wiki answers of a minimum length are eligible