Ultraviolet rays

What are ultraviolet rays?

Ultraviolet (UV) rays are oscillations of electromagnetic energy consisting of energy packets or photons that oscillate at various frequencies and manifest themselves with various properties.

The wavelength of ultraviolet radiation is between 100 and 400 nanometers (nm).

Ultraviolet radiation has great photoelectric and photochemical activity.

Ultraviolet therapy is a form of phototherapy used in Physical Therapy for its great benefits on cells and cell structures, as well as for its biological and bactericidal action.


  • UV A: They go from 320 to 400 nm, it is the least energetic part
  • UV B: They go from 290 to 320 nm
  • UV C: They range from 200 to 290 nm. They are characterized by their bactericidal action.

UV optical laws

The optical laws that apply in ultraviolet are:

Reflection: The reflection of the UV varies according to the surface:

  • On Polished surfaces: It is specular
  • On irregular surfaces: it is diffuse
  • On dark surfaces: there is less reflection
  • On glossy surfaces: There is more reflection


Dispersion: It occurs when reflection and refraction occur in an irregular environment

Transmission: UV rays do not need a means to transmit

Penetration: When UV rays reach the skin some are partially reflected and others are dispersed in the skin before being absorbed.

Absorption: When absorbed UV rays produce an insignificant amount of heat.
This absorption produces interactions between energy and molecules that can be molecular excitation or molecular dissociation.

Biological action and cellular effects of ultraviolet rays

  • Photochemical properties that allow the separation of two oxygen atoms.
  • Vitamin synthesis: Ergosterol and 7-dehydrocholesterol provitamins are converted into vitamin D3 by ultraviolet rays.
  • Stimulation of mitosis: Produces corneal stratum hyperplasia.
  • Bactericidal action: With high doses of UV B, but mainly with UV C, this effect is achieved, so they are used in infected wounds and bedsores.

– Other effects are:

  • Protein denaturation
  • Intra and intercellular edema
  • Skin pigmentation
  • Stimulation of keratogenesis
  • Carcinogenic action  

The filters for UV rays in our body are melanin, keratin, lipids and epidermal proteins


To obtain the necessary dose it is necessary to calculate the erythema dose, which is the necessary amount of UV radiation to produce an erythema under established conditions.

For this, the test is applied in an area that is comparable to the area to be treated in case of partial treatments, if the application is general, the test is done in 100% sensitive areas.

The UV meter is placed on the skin, the first hole is opened and irradiated for 1 minute, the second hole is opened for another minute, so that the first hole has now received two minutes of radiation. And so on until completing the 8 or 10 minutes.

The skin is examined 8 or 24 hours later and the degrees of the erythema found are determined. The treatment will then be carried out with the radiation time that the therapist considers appropriate to obtain the necessary effects that he seeks.

Indications of ultraviolet rays

  • Psoriasis
  • Acne cyst
  • Rickets
  • Ulcers by decubitus
  • Wounds
  • Sun tanning

Contraindications of ultraviolet rays

  • Albinism
  • Atrophic skin and scars
  • Eruptions due to herpes simplex
  • Skin carcinoma
  • Systemic lupus erythematosus
  • Xeroderma pigmentosa
  • Severe Mellitus Diabetes
  • Pulmonary tuberculosis
  • Severe cardiac disorders
  • Abnormal acute skin irritations
  • Known photosensitivity.

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