http://www.medizinauskunft.de/artikel/aktiv/r...
Als Sonnenblocker werden Lichtschutzfaktoren ab 20 bezeichnet.

www.primary-care.ch/pdf/2004/2004-38/2004-38-205.PDF
Heutige Sonnenschutzmittel, insbesondere Sonnenblocker, bieten zwar einen
wesentlich besseren Schutz gegenüber der UV-Bestrahlung als früher.

http://www.greenpeace-magazin.de/magazin/repp...
2. Absatz

Zur englischen Schreibweise bietet http://www.dict.cc/deutsch-englisch/Sonnenblo...
Sonnenblocker {m}
sunblock
sun block
sunblocker
sun blocker

Für dict.occ ist 'Sonnenblocker' als deutsches Wort bereits wörterbuchreif, für Leo auch?
Warum Kennzeichnung als [amer.]?

sun-block [med.] - der Sonnenblocker is already in LEO
Dictionary: Sonnenblocker

I would, however, prefer to see "sunblock" or "sun block" as one word or two separate words and not the hyphenated version given at present - more of a "wrong entry" than a "new entry".

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2004, 2000 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

"sunblock also sun block (sŭn'blŏk')
n.
A preparation that prevents sunburn by filtering out the sun's ultraviolet rays, often purported to offer more protection than a sunscreen."
http://www.answers.com/sunblock&r=67

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company.

"sun block
n.
A preparation, as of PABA, that prevents sunburn by filtering out the sun's ultraviolet rays, usually offering more protection than a sunscreen."
http://www.answers.com/sunblock&r=67#copyright

Nor is the [Amer.] flag necessary
http://www.netdoctor.co.uk/travel/diseases/sa...

Cf.
http://en.wikipedia.org/wiki/Sunscreen

I agree with Marianne on all points, so would suggest changing the existing entry as shown above. The -er is wrong in English AFAIK, and so is the hyphen.

The point is that a sunblock almost totally protects your skin from sunburn, unlike a sunscreen (medium protection) or a suntan lotion (limited protection). The old-fashioned one was zinc oxide, a thick white cream; nowadays it's usually just something with an SPF of 30+, which I believe is the maximum rating allowed by the FDA in the US.

Wikipedia also lists 'suncream,' which AFAIK is not used at all in AE.

Whether 'Sonnenschutz' or 'Sonnenschutzcreme' is also a possible translation of 'sunblock' is for German speakers to say.

AHD:
sun·screen
A preparation, often in the form of a cream or lotion, used to protect the skin from the damaging ultraviolet rays of the sun.

sunblock

VARIANT FORMS:also sun block
NOUN:A preparation that prevents sunburn by filtering out the sun's ultraviolet rays, often purported to offer more protection than a sunscreen.

Bin gegen die Domäne [chem].
Der Sonennblocker ist ziemlich neudeutsch - ich würde sowas immer als Sunblocker bezeichnen (es gibt für Sunblocker 97.000 +Treffer in .de, für Sonnenblocker 530+) - und bezieht sich auf Sonnenschutzmittel mit hohem Lichtschutzfaktor.

Nach AHD weckt die Bezeichnung sunblock die Erwartung, er sei effektiver als sunscreen, das muß aber nichtder Fall sein.